Ive had a problem with a hunting idle right at start up for quite some time now. I went and took out the p and neutral +100 rpms and raised each rpm up increments of a 100. It helped, but the car really hunts for a while till it calms down. I noticed also that the vacuum jumps and falls in conjuction... What should I look into in order to correct this problem.
What is the correct mL for 383 ci...? My comp was set at 0 cylinders and 714 ml, so according to my calc. that would be 780 I left cylinders alone, that seems strange.
Paul

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90 Red Convertible
100k running great
ZAINO!!!
383 Stroked.... LT4 Hot Cam... Forged Elgen Pistons Scat 9000 Crank Elgen 5.7" rods New Lifters w/ 1.6 Rockers and hardened Pushrods Super Ram Intake Hooker Headers and Y pipe into Gutted Cat with Monza Mufflers (WAY TO LOUD!!) Adj Regulator K&N Shift Kit High stall converter 160 termo, ZR1 Rims.... Red Calipers....Alpine head unit, Kenwood 6x9 4 ways, Polk DX 6 1/2 compnents, MTX 240 amp, Viper 550 alarm,


www.corvetteforum.net/c4/nomar116/

 

Make sure the timing values on the main spark table are all the same in your idle region.

Cylinder volume should be 784ml.

 

Im going to change the values over to 784... Nonetheless the car really really hunts when I first start it or shift from park to drive or reverse... Removing the 100 rpm drop and raising all the values 100 didnt help... It almost made it worse until the car warms up.. Can anyone offer some suggestions on how to correct this problem?? I dont know that its spark but pretty certain its fuel if not just a constant or something...Pretty desperate for some experience here...
Paul

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90 Red Convertible
100k running great
ZAINO!!!
383 Stroked.... LT4 Hot Cam... Forged Elgen Pistons Scat 9000 Crank Elgen 5.7" rods New Lifters w/ 1.6 Rockers and hardened Pushrods Super Ram Intake Hooker Headers and Y pipe into Gutted Cat with Monza Mufflers (WAY TO LOUD!!) Adj Regulator K&N Shift Kit High stall converter 160 termo, ZR1 Rims.... Red Calipers....Alpine head unit, Kenwood 6x9 4 ways, Polk DX 6 1/2 compnents, MTX 240 amp, Viper 550 alarm,


www.corvetteforum.net/c4/nomar116/

 

Im the only one responding here... Lol But Im starting to think I should play with spark advance. Im pretty sure not enough advance is causing the motor to die. What do I need to look for here... Im pretty confused on the topic, and Traxions article among many others either glaze over the topic or seem a little to advanced. I have the readings from datamaster, just need to make sense of all of it... What should I look for at idle in terms of advance, and whats the difference between advance in terms of the chip, and advance in terms of the physical 8* adv Im running now.
Paul

------------------
90 Red Convertible
100k running great
ZAINO!!!
383 Stroked.... LT4 Hot Cam... Forged Elgen Pistons Scat 9000 Crank Elgen 5.7" rods New Lifters w/ 1.6 Rockers and hardened Pushrods Super Ram Intake Hooker Headers and Y pipe into Gutted Cat with Monza Mufflers (WAY TO LOUD!!) Adj Regulator K&N Shift Kit High stall converter 160 termo, ZR1 Rims.... Red Calipers....Alpine head unit, Kenwood 6x9 4 ways, Polk DX 6 1/2 compnents, MTX 240 amp, Viper 550 alarm,


www.corvetteforum.net/c4/nomar116/

 

I assume you have ruled out any vacuum leaks. Have you performed a minimum idle air adjustment? What are your IAC counts at warm idle? Is your idle moving before or after your IAC counts are?

 

I agree with 89vette,you did'nt mention it
but normally correcting that has solved my problem in the past.(make sure car is completely warmed up .

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87 IROC WITH 409(.040 OVER400) MINIRAM,NOS(125HP)TRICK FLOW PORTED HEADS,C.C.CAM,FLOWTEK HEADERS,CUSTOM PROM,MODIFIED 700R TRANS,2400 B&M CONVERTER,3.73POSI REAREND.
LOOKING FOR THE 11 SEC. ZONE.current ets.12.39@114 mph

 

Well Im currently having the troubles when the car is cold, again right after startup. Lets ask this question, what do you guys consider warm..? I have a manual fan switch right now, and rely solely on that, so I have no idea where I want the temp of this motor... As for the IAC counts let me give you some numbers...

At only about 60* C I took my latest reading with a slight change in the VE table... Found that in closed loop when the idle would rise, the IAC count would lower, when the idle fell, the IAC count would rise... Maybe this is backwards but thats what the Datamaster seems to indicate. Again not a warm idle, I can take that reading too, but this is where Im concerned. Also I had a steady Spark Adv of 23- 28 deg and a BLM constant at 118.

Same chip, closed loop at 70* C
The BLM was at 108 with the Integrator holding between 120 and 103...

The Spark advance varied from 25 to 18 or so
The IAC Count seemed steady between 71 and 69
I did notice that at one point, the idle slightly stumbled, the IAC Count started dropping made it all the way to 61 with the car stumbling and then made its way back down and the car held a decent idle. Again most of this is just to get a cold idle going right, probably most open loop I imagine. Can I add spark advance or should I just subtract fuel... Whats an advantage to either method?


Without a corrected idle (IE Removed the park neutral step and raised 100 RPM and w/o VE mods) The car idled at 625 unstead of 725 with a steadily falling Integrator and Spark Advance much the same as before...

In conclusion Im making head way, and if theres not much help (I know Im trying hard to uncover good sites and archived stuff...) So if nothing else Im documenting my struggles step by step...
Paul

 

You didn't answer any of my previous questions. If your BLM is 108 at idle in closed loop and your INT is 120 to 103 you are very rich. Get that idle fuel dialed in better. From what your describing to me with your idle it sounds like surging to me. I'm not real sure what causes this, I always thought it was a vacuum leak.

So what I would do is not add any spark but get that idle fuel in line. Do the obvious first. Like I think I told you before, I used to be in your shoes before and I hated when people wrote me posts like I am doing right now (no offense Grumpy) but that is how you learn.

Jason

 

I agree with Jason that, besides not addressing the issue around the IAC - you are running extremely rich...verge of an O2 Sensor Rich SES code.

This could be a major part of your cold start problem because in cold start, you are in open loop relying on the tables - and your tables are excessively rich. To further compound this, cold start generally richens the mixture...the last thing you need.

I would do as Jason suggest, get your mixture to more reasonable levels and then work on the IAC - both physical adjustment and within the IAC Step Positions vs Coolant Temp.

 

The reason I avoided that question of a warm startup is simple. If I get the car warm it idles fine. Surging fits a little more than hunting, none the less I agree Im running rich. Just more work on the VEs I guess?? I already reduced by the values once.... Ill do it again though and check the results... We'll get there eventually.
Paul

 

Well I went out and took a better longer more accurate reading. I waited for the car to reach 90*C. After 60 sec the car's idle ABRUPTLY changed. Not a change to closed loop, that happened 10 secs earlier, but the car quickly gained what I would consider a stable idle... at around my set of 700 rpms, IAC Pos locked at 65.

Now Im using Datamaster and the use L Term and S Term....

I was under the impression the Integrator had to reach 80 before the BLM would fall one value, however, it seems to act a little differently... I noticed that the BLM could suddenly fall one or two numbers with the Integrator at around 112 or so...

I noticed the car really struggled in open loop (@ 70* C) Neither the BLM nor the Integrator reported during this period...I think on previous runs that wasnt the case.

Then when entering closed loop, the Integrator would fall to around 115 then suddenly reset to 128.... Then fall again then reset... All the while the BLM remaining at 128. Then the minute the BLM began to fall the car steadied it's idle....

Im still running rich after this point BLM of 108 Even though the Integrator did not once reach th 80 minimum value... I guess Im just confused... Its recording at the fastest speed and Im beginning to be concerned maybe this is a bad chip...???? I dunno something seems funny but Im just asking doesnt seem to match up with what Ive been reading.
Paul

------------------
90 Red Convertible
100k running great
ZAINO!!!
383 Stroked.... LT4 Hot Cam... Forged Elgen Pistons Scat 9000 Crank Elgen 5.7" rods New Lifters w/ 1.6 Rockers and hardened Pushrods Super Ram Intake Hooker Headers and Y pipe into Gutted Cat with Monza Mufflers (WAY TO LOUD!!) Adj Regulator K&N Shift Kit High stall converter 160 termo, ZR1 Rims.... Red Calipers....Alpine head unit, Kenwood 6x9 4 ways, Polk DX 6 1/2 compnents, MTX 240 amp, Viper 550 alarm,


www.corvetteforum.net/c4/nomar116/

 

Another post.... I noticed that when I did this run it surprised me at the 128 BLM but I also realized that this was the first time disconnecting the battery and all my previous runs where steady in open loop just at various BLMs. Im thinking will that make a second start up a little more stable...????? Just brainstorming and documenting my findings for the other newbies like me to come... But Im hoping for responses whenever possible

 

It really seems like its a vacuum leak or something, but again Im starting to think its only in open loop which just means the chip is off, once the car gets out of open for 10 secs it idles fine. I cut the VE tables down even further in the mid to low 40's now on many idle 50 kpa values... Still hunting though not as bad... What is a bottom line sorta number where Id know Im hitting in the wrong place???
Paul

 

Paul,

I'm working on a cold start idle problem that began when I put on a 52mm TB. When cold, my IAC is at 160, after its run for a short time, the IAC drops to 60 and idle is perfect. Don't know what triggers the computer to start adjusting the IAC, but maybe I should just lower the park position?The engine temp hasn't risen much (75*F to 82*F) when the IAC changes and it's still open loop mode. When cold the INT was 128, BLM was 129, and the BLM cell was 4. Later when it was warm, the INT was 127, BLM is 126, and the BLM cell was 4. It's dialed in pretty nicely when warm.

I can plot my engine RPMs when cold and see typical oscillations between 550 and 800 RPMs. The MAP reading oscillates 40 and 60 kpa, and the timing oscillates between 30* and 32*. If the oscillations get going too far then the RPMs drop below 300 on the low end and the car stalls. MAP readings reach highs of 80 kpa, and the timing drops to lows of 22*.

My timing table has 16.5* for 600RPM, 40-60 kpa, and 20.4* for 800 RPM, 40-60 kpa. I'll try making a larger region the same flash a chip tomorrow and let you know if it makes a difference.

Joe
92 Z28
http://home.cfl.rr.com/shuhy/chevy.htm

 

Joe, haven't seen you around on the F-body third-gen list in a while! Going to Memphis next year?

When your engine is cold, the IAC motor is maxing out trying to bring the idle speed up to what is being requested. To help it out, you'll need to crack open your TB blades a little using the adjustment screw. This will lower the warmed-up IAC count, which gives the IAC motor a larger range to use when the engine coolant is cold. Currently, the IAC is only going between 60-160 instead of, say, 15-160. I had the same problem when I programmed a higher idle speed for my old 305, and the same for my new 355 with a 750-rpm idle.

Also, there's a table for adjusting the closed-throttle timing in which you'll want the values to be all the same in the rpm range where your engine idles. It also might help to make the timing the same number in the rpm/MAP area in the main spark advance table where your engine idles, just to make sure that it's a smooth transition coming off idle. You can also bump up the timing in both tables to 24-28 degrees to get more vacuum with the cam you have. I'm running 30 degrees total timing to tame the LT4 HOT cam in my 355, giving me 2 inches more vacuum compared to 18-20 degrees.

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Greg Westphal
'87 IROC 355TPI/A4

 

I would keep adjusting the VE tables until your idle fuel is in line and then tune from there. If all of your BLM cells are 108 or really rich, then you may want to lower raise your injector constant. What is it set at now and what size injectors are you running?
Your welcome to mail me off list also if you like. I don't get a change to visit this board everyday.

 

Damn, just wrote out a post and sacrificed it to the cybergods because I forgot to put in the username/password.

Anyway, how's it going, Greg? It's definately been a while. I've been lurking here as I work on tuning the car. First tuned for heads and cam, then rework for the 52mm TB, and more rework if I get some 1 3/4" SLP headers to replaced the Edelbrocks. Don't know about Memphis, I'd be tempted to take the 2002 SS if I went.

I've tried changing the idle screw in the past, but the point where the it idles nicely when cold makes the warm idle RPMs way too high. I set it again tonight, and I'll test it once the engine cools down.

Changing the main spark table had no significant effect on cold idle, I've modify the closed throttle spark table now (24* for 400 and 800 RPM) and I'll flash it at work tomorrow.

The way I understand it, the IAC being at 160 is allowing too much air in, hence the smooth idle once the IAC drops to 60. I've increased the requested cold idle RPM to get more gas injected (and the IAC can't allow any more air in) and this helps some. When I lower the cold RPM, it idles even worse. By opening the butterflies more to get lower IAC when warm, it seems I'll get even more air at cold idle (IAC at 160 + opened butterflies) and make it worse. Am I missing something here?

Joe
92 Z28

 

Ill email you soon 89Vette...Im thinking of playing with a little idle timing too because my timing oscilates between 16 and 22* with a LT4 Hot cam and a huge breathing intake and motor in general.... I really think that could be one of the problems right there.... I have taken alot of fuel out tho, and have the BLMs alot closer, I have noticed that the L and S term (opposed to BLM and INT) of Datamaster, seems to adjust more on its own and in real time, IE it doesnt take a value of 80 to lower the L term one digit or 4 for that matter.... It adjusts as it sees the motor go lean and rich... is this correct or is there a different explanation.
Paul

 

Joe, it sounds like your engine wants a higher idle speed when it's cold, maybe even more than what the computer is requesting. With the IAC at 160, not enough air is getting into the motor to bring the idle speed up to what the computer wants, which is why your engine is oscillating when it's cold. When the IAC drops to 60 (or wherever), the requested idle speed will be lower since the engine has warmed up some, plus you might be going into closed loop by then. HTH...

------------------
Greg Westphal
'87 IROC 355TPI/A4

 

Nomar,

I've noticed the eratic timing with my Datamaster also, and was somewhat puzzled by it. And the Lterm/Sterm corrections don't follow the pattern I thought they should, like you've mentioned. Any idea what the Lterm adj. (I think that's what they call it) is? My Lterm adj. moves about as fast as the Sterm counts. Thanks.

Regards,
Gary Anderson

 

This is the first I have heard of such a table. Do you know if there is a similar one in the $6E code? If so, I'll have to contact Tuner Cat for a new TDF...



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'87 IROC 5.7l TPI - original owner!

 

Nope, no such table in the $6E code. I just change the timing in the main spark advance area where my engine idles using RPM and LV8 data to give me the proper range.

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Greg Westphal
'87 IROC 355TPI/A4

 

Just an update. I haven't fixed the idle problem yet. I adjusted the idle air screw without any major cold idle benefit. I then noticed that my idle adjustment pushed my TPS to .65V. I adjusted my TPS back to .55V at idle and now my IAC drops to 0 at idle when warm. Problem is I idle at 950 RPM in park (comptuer requesting 615RPM) due to the idle air screw adjustment. I still surge at idle to boot.

I lowered my IAC learn temp, but even with my 160 thermo stat I'd get to 195 idling thru my neighborhood, so it should have been learning with the default setting anyway. I'll let you know if I make any forward progress, or post on my lack of progress periodically.

Joe

 

A question about IAC.... Would that cause the car to just die at a cold idle if its taken from park into say reverse... I had thought the idle was pretty close, experiencing only a slight drop in rpm with the closer BLMs but this evening the car had had only about 45 secs to warm and it just died when I went into reverse.... Thoughts
Paul

 

Try playing with the Stall Saver parameters. Also, there is another IAC Step Table vs Coolant, that I believe TunerCat has just added.

When your engine is cold, you rely solely on your tables including the IAC. Sounds like the defaults in the eprom are off; or your IAC adjustment is off.