My engine has developed a characteristic as of late to search for and idle rpm. When the engine is warm, tranny in park, it will rev up to 700-800 and back down to 550-600. Then it will go up and back down. Just like it wants to sit at 650, but it can't.

Any ideas?

I have not really change anything on the motor this year, and this surge has show up.

Along with the surge, I have also noticed a rough idle, but I think I solved that tonight. But the surge is still there.

My combination is as follows:
5.7L block, 1987 5.7L PROM, stock MAF,
edelbrock RPM heads, 1.5 intake, 1.6 exhaust rockers,
ZZ3 cam, flattop pistons (9.75:1 measured comp),
52mm TB, ported upper plenum, blended stock runners,
AFPR, NO EGR, NO TB coolant lines

This year, in my quest for a smooth idle, I have changed/checked the following:

- replaced TPI gaskets
- re-torqued intake gaskets
- Checked for vacuum leaks
- Checked timing - 10 degrees base (sames as it always was)
- replaced IAC
- replaced MAT
- swapped ESC with spare
- tested a backup ECM
- tested a 1988 5.7L prom
- checked knock sensor - scanner shows counts when you tap it
- scanner does not show anything out of the norm
- plugs all appear same
- plug wires are MSD 8.8's. Visually look ok
- coil was new last year
- HEI module was new last year
- set minimum idle tonight
(when I did this, with the IAC disconnected it still surged! It has to be spark or fuel then!)
- set TPS
- checked PCV

One good thing. I believe my ESC was going south. The one I took out seemed to have some melted plastic in the center, like it got hot. With the swapped one, the engine seems to idle as usual when stopped at a light, and tranny in gear.

Good news is that I think my rough idle when in gear is gone. But the surge is still there. Just curious what it might be.

Long post, but maybe someone has some ideas.

Mark.

 

Did some searching on "surge" and found some good info. Just posting it here for reference.

- one person had a fuel pump going south. I need to verify my fuel pressure to see what mine is doing.
- Another person had a bad MAF.
https://www.thirdgen.org/techbb2/sho...ighlight=surge
- Need to check that the MAF is working correctly.

I'll add more stuff here as I find it. Perhaps someone else can benefit from this stuff.

Mark.

 

More testing today. Still surges from 600-750 or there abouts.

- base timing is 8 degrees (set it down from the 9 or 10 that it was).
- TPS is .54
- MAF burn off works
- voltage is 12.5 with no charge, and 14.5 charging
- checked scanner again, nothing out of the norm.

Perhaps I am just at the end of the stock prom calibrations ... although I could have sworn it ran fine last summer. Maybe I never notice the idle.

I hope to do some more digging in the prom tables in WinBin to see if I can find something that might cause the idle surge. Maybe there is an EGR thing going on, and since I have no EGR, the surge is happening. Although the lack of EGR of has never set a code.

Mark.

 

mark, it will be interesting to see what or if you find anything out, mine has surged like that from time to time, nothing constantly, one time it surged so much while in drive at a stop light I thought it was going to try to launch into the car infront of me, only happened that one time, so I have no idea where to look, and since it happens rarely I dont worry about it, but if you find a culprit maybe that will help correct the problem

 

I have the same problem when the car first starts. I set the idle up some, which helped quite a bit. It idles about 900 in park, and around 6-700 in gear. A little prom tuning would probibly be the best way to fix the problem, but I still don't have the equepment to do that.

 

The park/Neutral switch can also cause a hunting idle condition. There are just so many things that can cause or contribute to this condition and the troubleshooting for them are too long to list here. Need to invest in some good troubleshooting books.

 

Mark,
I know you checked the IAC already, but I saw the following in a library book I just got. It describes the IAC operation. Pay close attention to the last 2 sentences, maybe that's what you need to do.

"The IAC or idle air control valve mounted in the throttlebody is designed to control engine idle speed and prevent stalling due to changes in engine load at startup. It also provides cold start fast idle during the warmup period. A conical valve called a pintel moves in annd out against its seat to control the amount of air being bled past the throttle blades. If RPM is too low, more air is bypassed; if RPM is too high, less air is bypassed. The ECM moves the valve in small steps called counts. Engine idle speed is a function of total airflow calculations based on the IAC valve position, throttle valve opening, PCV flow, and calibrated flow loss to vacuum accessories. If the idle air adjustment is off it can be reset by stopping the engine. Depress the accelerator pedal slightly and start the engine for 5 seconds, then turn the ignition off for 10 seconds."

 

Thanks, Sciguyjim.

The jury is still out on what is making it surge. I could have sworn, with the IAC diconnected, it still surged, making the problem something with spark or fuel.

I thought when I set base timing the engine ran smoother, but I need to check this again and see.

I suppose I could disconnect the IAC, and the timing set wire and see how it idles. In therory, it should idle at 500 rpm or so.

I am at the point, I am just trying to rule out different things that are causing the surge. If I can narrow this down, then I can look for the cause. I know, sounds like a backwards way to do things.

Mark.

 

FWIW, a surging idle is characteristic of a lean condition IIRC. Are you getting extra air flow (leak) thru the PCV port? Is the EGR connection completely sealed off? Are all the injectors known good (especially the ones on the bank away from the O2 sensor)?

What IAC steps is it idling at? What are the idle BLM/O2 readings? Have you tried cranking in a little more fuel press?

(The rest are all ECM changes, and I have no first-hand knowledge of MAF units.)
I have an SD setup on mine, and when it surges I just crank in a little more injector pulse width at idle, or (theoretically, since I've never had to do it) raise the injector low PW constant a little. If that didn't work I'd consider dumping a little timing out of the idle area - but I've never had to.

Idle is a PITA. With the injectors running at less than 2 msec, it doesn't take much of a change to throw them from lean to rich.

HTH

 

Here is what I did to cure my surging idle.I unplugged the IAC. I used the ARAP.bin which has the EGR turned off by maxing out the tables to 255 in all of the categories. I then went in and changed the Min temp for Closed Loop enable to 110* C so that in effect the car never got to closed loop. This, in my thinking got rid of the possibility of a vacuum leak because with the car always in open loop, the car never surged at all. Not at stoplights, not at idle or part throttle cruise. The only thing that I know of for certain NOW is that I either have a few bad injectors or an exhaust leak. or a misfire problem... causing a lean misfire/false rich condition.

If you would like I'll send you an ARAP.bin to look at but you won't be able to use it in your car since my car is a $6E and yours is a $32 I believe. Email me for my .bin. You can obviously look at what is changed on my .bin and try it with yours.

 

Lean condition ... I'd buy that.

My BLM floats around 128-132, so it seems to be OK. I run a heated O2 sensor, only two years old. The scanner shows the crossover counts, so I take that as a good sign. At 1000 RPM (ALDL mode), my IAC is around 50. I have set base air flow the other day, which actually required me to turn it in, and thus raised my IAC from usual.

The one thing I have not checked yet is the fuel pressure. Tried that on the weekend, and got fuel everywhere ... damn fitting is such a pain. I'll have to save that for another day or just order the fuel rail pressure gauge.

My injectors were all cleaned and tested 2 years ago when I put it together, but I park the vehicle in the winter, so there could be plugged injectors. All plugs read the same. I would expect a bad injector to show up on the plugs.

I can try to plug the PCV and see what happens.

I am curious what EGR is doing. I don't have EGR passages in my heads, and I have unplugged everything connected to EGR, including the +12 feed on the fuze box. No codes ever. PErhaps there is an EGR mode that is happening when the engine is hot, closed loop, etc. And it is "expecting" EGR, but since I don't have it ...

I've been avoiding the prom programming due to my lack of time to spend on it. I have worked with WinBin and read through my Bin and my spare bin, and I find it rather interesting. I suppose I just need to order the pocket programmer and get going. Then my idle problems may just go away.

Mark.

 

Thanks, I have the ARAP bin already. Planning to use it when I get around to doing my own. Right now I run a 1987 bin (one of the last ones from 87). IT runs surprizingly well. I also have a 1988 bin (again, a late 1988 bin). What I found interesting when comparing them in WinBin was that the spark tables were hugely different. The 1987 was a text book style modelled after a mechanical advance. The 1988 use the power enrichment mode to add more spark, as well the spark tables were more wavey than linear step. I might just order tunercat after all and spend time researching what is going on.

MArk.

 

It's probably some sort of MAF issue, but it's worth checking the oter items anyway:

A weak injector on the bank away from the O2 sensor is very hard to spot without testing them.

Dunno what your intake looks like - on mine there is an external EGR pipe that leads back to the intake (under the plenum). When I want to test without EGR, I put a solid plate over the pipe inlet, to seal the system off from outside air completely - then I know nothing is leaking thru the valve.

One other (esoteric) idea - one guy I know had a bad CCP solenoid (actually it was wired in backwards) that bled air into the intake at idle. Took some weeks of head-scratching to find that one.

HTH

 

The older bin calibrations all had that idle hunt problem. Switch to an 89 bin (like the ARAP), disable your cold start injector, and you will solve your hunt problem.

Also cures the "high rpm at startup" problem where it takes forever for the idle to come back down at startup. I had the same problems on my 86 stock motor even before I started doing mods.

EGR should not come into play at idle.

 

it seem that you have checked everything. i thought that it might be your injectors. but you said they are good. you should all so check your fuel presure and change the fuel filter at that time too.

 

Ongoing saga ...

Latest updates ... for those who might search the archives and find this useful.

My Goal: to determine which device was making the engine hunt for an idle. Was it the IAC, the spark, the fuel, the air, act of ***?

My tests:

Engine warm, idle ranged from 650-850 (hunting!).

1) disconnected and plugged PCV. Idle still hunted.
2) MAF disconnected - ran rougher, set a code, idle still hunted once it settled down.
3) disconnect the set timing connector. - set code, idle rougher, still hunted.
4) AFRP - removed vac line to see if higher pressure made a difference. - No change in idle, but testing with a scanner confirmed that pulse width did drop with the higher pressure, and the crossover counts decrease initially. Extra fuel made a difference, but not to the idle hunting.
5) Disconnect IAC - used the set min air test. With IAC disconnected, the idle hunt was still there, but not as wide. I expect that if the hunt was 20% at 650, it just 20% at 500, so not as large at a smaller scale.
5a) disconnected the set timing too. At first it seemed stable once I got it to idle. But it still hunted, again on a smaller scale.

Conclusions ... well I have 3 codes floating in my ECM now. It still hunts for an idle and I am no further ahead.

Next Steps: Well about the only thing I have not looked at is the actual distributor. I have another one, so I think I will clean it up, replace what needs it, and swap it in. It's a longshot, but I also wanted to repalce my dist gear with one from a 96 vortec motor. Suppose to be harder and made for high volume pumps. I recall my gear shows wear after 10,000 miles.

I could have a bad fuel injector or a few bad ones. Perhaps they are flowing poorly at idle. I had them cleaned maybe 10,000 miles ago. Perhaps they are just old. I have wanted to upgrade to 24's, but only when I get into burning my own chips. I am not sure my combination needs 24's yet.

Well ... for those who are interested, I hope you enjoy my testing. The funny thing ... my mileage has been great.

Onward I go.
Mark.

 

Oh yes ... one more thought. Perhaps my cam/engine combo just needs a higher idle. I know larger cams usually need a slightly higher idle. Maybe the stock 650 just is not cutting it. Something to research.

Mark.

 

Have you checked the park/neutral switch? There is a pin check you can do on it for hunting idle, its in one of my FI troubleshooting books.

 

Speaking of FI trouble shooting books, what are some "good" ones. I have some manuals that are specific to my car but the trouble shooting sections are a joke(chiltons, haynes, motors). Any suggestions?

Thanks

 

More testing ...

Tonight ... to O2 or not to O2.

So I fired it up and let it warm up. The idle dropped down to 650 in a matter of minutes ... them temp gauge barely moved. I have a heated O2 sensor, perhaps this helps.

Anyhow ... the hunting began.

I turned if off and unplugged my O2.

The result ... A LARGER HUNT! Now it hunted from 500 to 1000. Wow I found something that made a difference, ok not to the good, but none the less SOMETHING!

So can a lazy O2 cause the idle hunt?!?

My O2 is two years old at least. Maybe 10000 miles, but I think that is high.

I even tried to run a seperate ground to my O2, but I could not see a difference. The darn thing jumps around so much. I thought I would see a higher average, but hard to tell.

Onward and backwards.

Mark.

 

Hey Mark, something I just thought about as to why the "hunt" got worse when you unplugged your O2, since unpluging the O2 makes the ECM stay in OPEN LOOP, I notice a table in the eprom in which fuel is added by cerrtain % more at various temps while in OPEN LOOP, anywhere from 5 to 20+%.
So when you unplugged the O2, more fuel was being added because of OPEN LOOP conditions.
If you have a leaking injector, then the O2 was leaning things out some in CLOSED LOOP, but in open loop, no leaning and more fuel, thus a rougher idle.
As soon as the verdict is out on the cheap Accell injectors, I'm buying some, either them or some MSDs.

 

that makes sence because when i run at the track with my o2 sensor unpluged i run 2-3 tenths faster

i think i have some leaking injectoer or the 14 yearold injectoer need replacing

 

I have the exact same problem. However I posted a similar question to this already. I described it differently. Someone in there posted some troubleshooting and correction options. It's under tech/general engine as here's a weird problem. It's worth a look as there is alot of good info in there on this problem. I am going to do some of this stuff this weekend and see what happens.

 

Hey Mark, did you ever find the cause of your surging at idle?
Well, I changed my injectors Friday night and finished it up this morning, using the 24# Accells, reburned my eprom for them and re-enabled my O2 since I've had it in OPEN loop for the last few weeks....and whala..surging cured!!
Now I'm running very very lean cause I've been cutting fuel in the eprom for several weeks before the bad injector got bad enough to cause the surging, so now I'm adding fuel and spark back in.
My guess is if your injectors are 10years old with lots of miles on them, then you have one thats toast.
Let us know what you have found.

 

Quick,

I am thinking mine are injector related too. Like you, I want to upgrade to 24lb ones, but that is a ways down on the list of need-to-buy items. Food, morgage, etc. are sorta higher on the list these days ... :-)

I am glad to hear that yours is running better, and thanks for your update. I have pretty much ruled out my problem to the inner workings of the distributor (timing is shifting erratically) or the injectors have a crappy pattern, or a few are weak.

I'll have to see what are the least expensive brand of 24lb injectors I can find around here.

I wonder if I could do the old trick of disconneting one spark plug at a time to see which cylinder causes the least amount of change? That would point out the bad injector. I'd be curious to see if that would show anything.

Mark.

 

I should have tried disconnecting one at a time to see what kind of difference it would make before swapping the injectors but didn't. I did pull off each wire on the injectors this morning while running just to make sure each was firing properly, and surprisingly, the motor did not start to run rough until I disconnected 3 on the same side!
So to test, I unplugged 3, then reconnected a single one of the 3 and made sure the motor smoothed out after reconnecting each, then discod the 4th with only 1 connected to verify the 4th, then did the same thing on the other side.
And BTW, all my old injectors had an impedence of 12.3-12.5 ohms while the new Accels were all 14-3-14.5. So there was nothing obviously wrong there with the old ones.
*
And if you go with the Accells, the top portion that fits in the rail doesn't seem to fit quit as far up in the rail as the stockers unless use use the second locking ring, but then they aren't tall enough. There no problem with them not going all the way up in the rail, as long as the o-ring is seated at least half way up the injector slot in the rail. Some people think the injector has to be crammed down as far as it will go, but there's nothing sealing it the further up it is in the rail or the intake as long as the o-ring is completely seated in both the rail and the intake ports, doesn't matter how far up they are in the port holes. And BTW, its the seal at the rail that has all the fuel pressure against it, the one at the intake only has vacuum so no fuel will come out on the bottom anyways.
This is just FYI in case you read a post not long ago about someone gringing down their fuel rail mount post so that the injectors would fit further down the port holes....don't need to do that, just use the top most lock ring on the injectors, with the Accels, its the only lock ring that goes completely around the injector anyway so you can use the original lock rings that attach the injector to the rail.
And the Accels were cheapest at $229 and seem to be very good quality as compared to any other...I was worried about that when I was looking at them and did quit a bit of shopping around.

 

Update:The surging is returning. Started just doing it very slightly after a day or 2, but now is almost like it was now that the weather is getting colder. May try a hotter thermostat as it is staying around 150-160 now. If not, to hell with it, I'll just go back to the OPEN loop programmed chip.
So maybe the injectors are not your solution...I don't know what else to look for for this problem since it doesn't do it in open loop when the O2 is not functional...

 

Well that still leaves a couple things. Perhaps the AFPR is not working and causing the pressure to fluctuate. Long shot.

Other than that, the distributor ... perhaps there is play on the reluctor wheel causing the timing to move up to 1 degree. I do recall watching my timing during the surge with the set timing connector disconnected ... I could have sworn it moved, but it is hard to focus on that strobe, and in my case you have to contort yourself just to see it.

I want to replace my dist gear with a vortec one designed for a HV pump. So I will rebuild my spare dist and see if that helps. My cam seems to dig into my dist gear slightly, which I believe is caused by the HV oil pump. So after a few miles, you can see a groove starting to form. Not huge, but more than the polish marks one usually sees.

Quick, don't you have an MSD dist? Or is yours a stocker?


Mark.

 

In my case, I would investigate the dist, but it runs fine when the ECM is in OPEN loop, which also eliminates electrical problems.
I've got a stocker dist, but it only has about 15k miles on it, but I do have a HV oil pump.
My next attempt may be to investigat a short on the O2 sensor ground.
Oh and the fuel pressure I already ruled out with a manual gauge hooked up and strapped to the windshield.

 

I tried to run a seperate ground to my O2 thinking it was bad, but it still surged.

Hmm HV pump ... stocker dist. Perhaps you and I have the "eaten" dist gear syndrom. I know that does not explain open loop, but perhaps in open look the idle is higher? I am at a loss as to explain it, my forehead is numb from banging on the table so many times.

It's so friggen cold here now, and my heater in the garage is not working yet, so my testing will be delayed a bit.

Mark.

 

On the O2, with my scan tool kooked up, I notice the O2 voltages fluctuate a lot from .012 to .940mV, the .012 seems a bit low and it seems to stick there for a while which even further makes me concerned, and its a brand new AC Delco. I've never seen O2 voltages so low down in the double digits on any car.
Yet the BLMs are still in the 124 to 135 range.

 

Are your IAC counts or injector pulses hunting in relation to the RPM hunting plus is the hunting a quick up and down or a long up and down.

 

Mine will hunt with the IAC disconnected. It hunts with the set timing connector disconnected. Even tested both disconnected. Figure that one out.

In my case, if I unplug the O2 the surge is wider, from 500-1000 rpm, instead of the 650-800.

As for the rate of surge, not fast, just slow. Perhaps 1-2 seconds to rev up or down.

Mark.

 

All of this surging everyone is getting with the O2's disconnected sounds like a bad injector/s. Think on it, if the surging is smaller when the O2 is connected it would be because the ECM is trying to control the AFR to 14.7, but take the O2 sensor out of it and the ECM correction is gone, making the surge worse.

 

I agree with that, however Quick6 put new injectors and his surge has returned. I believe it may be caused by a few different things. Injectors certainly seem like my problem, but I also suspect the dist as well. I might try the idea out of disconnecting one injector at a time and see if the motor idles worse or the same. Long shot ... but it might point out a bad injectors. I also thought that a bad injector would show up when reading the plugs, but mine looked the same.

Mark.

 

Quick way to check your distributor would be to hook ip a timing light and see of the timing fluctuates along with the RPM change, if not then I'd doubt the dist.

 

Odd question ... would you have access to a scope? It would be interesting to watch your injector pulse width when the surge happens. If it stayed the same, and it surged, it is mechanical rather than controled by the ECM.

 

Unfortunately I don't have access to a scope. As for as the IAC counts at idle, they are about 60-80 and I can't get them any lower as the idle screw is all the way in, if I try to reset it with the IAC unplugged, turning it out just a little causes the motor to die.
I'll investigate the timing with the lead disconnected and watch it with a light and see what happens.
I'll pay real close attention on my scan tool on the inj pulse widths to see how they vary when surging, but it may not tell me the actual reading since its a 8 or so frame a second sampling.
*
And as Mark, all my plugs read the same so I don't think its a single cyclinder type problem. With the O2 working its very lazy on throttle response and even has a slight surge at highway cruise and light accelleration. With the O2 not working, it pulls hard verywhere and only surges at idle. It wierd how it keeps getting worse the more I drive and that it went away for a very short time after changing the injectors.....
I don't expect I'll find the cause anytime soon, and I won't be having much time the next month or two to keep investigating so we'll see, I'll keep posting here if and when I find anything...

 

Have you tried removing the throttle body and IAC and giving the whole thing a good through cleaning? Pay particular attention the the IAC pintle bore, it always gets a good healthy carbon build up in it and can block off the idle passage in it.
I used Valvoline Syntech carb/throttle body cleaner on mine and it dissolved all the carbon in a matter of minutes.

 

I've cleaned mine, heck even replaced the IAC just for the heck of it. Still surged, even with the IAC disconnect it surged.

Very odd.

 

Another possibility here is a minute vacuum leak, possibly at one of the injectors. Since you had it "fixed" at one point by replacing the injectors, you may have inadvertantly disturbed the seal that was/is leaking, either at the injector itself or possibly on the fuel rail.
I would also check all of the places on the throttle body that could possibly leak, ie; top plate, IAC gasket, IAC housing, the rubber boot at the front of the T/B.

 

A vacuum leak was my inital thought, especially at idle that would make sense as to the way it is acting, but it surges a part throttle cruise and light accelleration, yet with the O2 programmed out in OPEN loop, it only surges at idle. Also, a vacuum leak should cause the BLM's to climb quit high at idle, which mine are in the low 120's at idle.

 

Another update: I decided to go back and try a version of the my eprom that I had back several months ago before the surging slowly emerged. I keep every version of the eprom file I've ever made, I was on the 51st versions, so I went back to version #25, all I changed was the injector constant since I now have 24 lb injectors. Reburned the chip and popped it in and it idled very smoothly, drove around a while, still idles fairly smooth, but definitely no surging. So I went back and copied my most recent version, #51, starting with the spark table and fuel tables and copied all of the values for 1000rpm and over, so essentially I have my most recent version except for below 1000rpms its using the old #25 version. Still idles smooth and cruise doesn't surge either with the O2 fully operational.
*
There's not many parms I haven't tweaked or messed around with on the eprom, so figuring out what exactly started causing the surge, and it was gradual, it didn't start surging for just changing a single parm, and it gradually got worse, the only parm I have significantly changed now at idle speed was the "IAC timeout steps vs. temp" table in comparison to my new version #52 which has all the things for 1000+rpms as the "surging" version, in comparison to the old #25 version. Don't know yet if that is the single item that may have effected this, but it could have contributed along with changes in timing and fuel, which at idle are now the old version before the surge came along.
*
Mark, now what that said, I don;t think you have been changing your eprom from what I recall, but maybe added some parts recently like TB etc that may have effected air flow at idle.
*
Its still not as strong as the OPEN LOOP program, but lets see where I can take it, and if it starts surging again, I'll post back.

 

Hmm, that's interesting. You might want to wait a week and wee what happens.

In my case, I don't recall changing much in the recent months. I did put a K&N filter in, but I can't see what my air flow causing a problem. I thought the idle was still poor even before that.

It's now below freeze here, and snow on the ground. My testing time will be quite limited, unless I cut those exhaust ports into my garage door and run the truck inside the garage. Don't laugh, I did debate this when I installed the new door.

As with most winters, I will probably take it apart for some odd reason. Perhaps I will have some spare cash and replace my injectors. Not sure really. I do want to rebuild a dist using the vortec HD dist gear, for two reasons. One the the wear I am getting on the dist gear, and second for a piece of mind.

Keep me posted.
Mark.

 

Hey Mark, did you ever fix this problem? I don't have a third gen but I have a Syclone that has the same symptoms as you describe and it's driving me nuts!!!! I came to this board for some new ideas or to see if anyone has a similar problem.

I have replaced my injectors and o2 sensor, my fuel pressure is correct with no bleed down. The only problem I can find is a vacuum leak at the TB shaft but I am reluctant to spend $200+ to see if it fixes the problem.

 

Hi,

I only got my truck back on the road a short time ago.

I never did track down the cause of the surge. I did isolate that it was NOT the MAF, IAC, or Spark. I suspect it is now related to spark (out of phase dist), worn dist gear, or perhaps clogged injectors.

At one point, I had it idling warm, surging, and I had the MAF, IAC and set timing connector all disconnected. It still surged! There was nothing left as input to make it surge. Thus I suspect it's in the dist, or fuel injector related.

I need to swap in a different dist and see if that helps.

In time, I will try this out.

Mark.

 

Hi Mark,

I also think its the distributor, I have replaced my injectors and they did not help.

 

Did anyone ever solve this problem. Ive got an 87 Z28 doing the same thing.Mine is a 350 bored 40 with .010 crank stock heads 24lb accel injectors 230 - 236@ 50 510 520 lift comp cam all new sensors motorvation custom prom 2400 BM stall 3.73 gear and 700r4 Fuel pressure @45 per accel instructions I didnt have the problem before I rebuilt 350 a month ago. It smokes at idle mostly but also during acceleration. Idle is rough and erratic it idles at 1200 rpm @ start up then after a 30 sec. drops down to 900rpm were i set it and jumps from 500 to 1000 and when put in gear will die unless you give it some gas. Timing is @ 6 BTDC as per motorvation.Plugs are R45ts to R43ts and Ive tried every gap known to man. oh yeah and 8 & 10 deg inital timing. The timing mark of course jumps with the idle but its not as bad with the EST unhooked so Im certain of the inital timing. Since I just rebuilt the engine I checked compression 155 to 165 0n all cylinders. Ive tried several fuel pressure settings no change engine has been broke in and dosent use oil or alot of gas.Will haul *** but smokes and idles poorly but no miss during acceleration.Ive built many carb engines to race first TPI just for street and occ. pony and **** burner humiliator but im getting discouraged any help from you EFI folks sure would help. oh yeah also has hooker comp headers and flowmaster no cat exhaust.

 

Just curious,

What PROM are you running?
What thermostat?

You sound like you have a few problems. The poor idle and smoke is one thing, the surge is a seperate problem. I'd look after the smoke and the stalling first and then worry about the surge if it is still there.

Check the obvious things. Vac leaks, air intake leaks around the MAF, plug wires (I had a split in my main one!).

what do your plugs look like?

Do you have access to a data scanner?

Mark.
PS. I am installing new injectors this weekend, so I will see if that solves my problem. I suspect it is still my dist., but who knows.

 

What prom I have no idea I hooked up with motorvation through summit racing. I called them up and gave them all the specs from injectors to gears and what i would be doing with the Z and they sent prom for $402. Thermostat is a 180 car running in the norms. The plugs are sooty on the no. 5, 4, & 6 the rest show normal firing. No trouble codes. Dont have acess to scanner but would like to have one. I put my original prom for 87 TPI 350 back in and the car does the same thing. I have been all over the engine looking for vac. leak with my trusty can of oil and soap and water if its got one I cant find it. I thought that was whats up initially but Im pretty confident thats not it. I scene were somebody had unplugged the MAF and that wasnt it I unplugged mine and the car dies is that normal no codes. You name it and Ill try it limited medic income but I want this car running right its my wifes if you know what i mean. Oh yeah car only stalls when it first goes into gear if you make it past that car starts surging and will eventualy die in gear while holding the brake. Car doesnt hesitate and runs great while moving but does smoke when you let off the gas or when it idles.