Hi Guys, I'm not sure if this is the right section to post this but everyone here was so helpful with my last post, I thought I would give it a try... A while back I had my 350 rebuilt (new pistons, cam bearing, crank turned, etc) and bored .030 over. Once I had my new motor in the car, I put my HSR on it and love the upper-rpm power! However, the car seems to surge about 200rpm or so in idle and feels like it may have a miss as well. My knock counts seem to keep going up regardless of what I have the timing or fuel pressure at (FYI, I had TPIS make a custom chip for my HSR install). I've tried everything I can think of but can't fix this issue. I've tried... *unplugging the MAF *unplugging knock sensor *unplugging the IAC *readjusting the valves *spraying carb cleaner on the gaskets to find vac leak *adjusting the fuel pressure & timing, *resetting the minimum air *new throttle body gasket *new wires/cap/rotor *unplugging the manifold temp sensor I did do a compression check on my engine and found out #1 is a little low for some reason. Could this cause the problem? Here are the compression results.. #1 - 161 #2 - 170 #3 - 186 #4 - 175 #5 - 170 #6 - 180 #7 - 170 #8 - 175 Any ideas would be GREATLY appreciated!!! FYI - timing is at 6*, fuel pressure is at 43psi (per TPIS), the TPS is at .58 and spark plugs are gapped at .035. Thanks a million guys!

Most of the time, a surging or hunting idle engine is caused by a vacuum leak. Check that out. Also, I would bump the static timing to 10* and complete the idle air procedure and idle RPM procedure. These are documented on the tech article page on the home page here on thirdgen.

EDIT: its called "IAC and TPS Adjustment"; under the IAC adjustment, where it says 450 RPM use 700 RPM (I have never been able to get my engine to idle or work right by setting it to 450 RPM)

EDIT: For the vacuum leak check, you could open but not lite-up a benzamatic (sp) propane tank and while the engine is idleing, move the nozzle around the intake system joints. If the engine suddenly speeds up, you have found your vacuuum leak.

Thanks for the reply doc!

I tried adjusting the timing today everywhere from 4 to 10* but it still had the issue.

I have previously used the tech article to set the minimum air and tps voltage.

Any other ideas?

Vacuum leak.

Or maybe (and this is a stretch) the stall saver is getting activated. This might depend on what idle RPM you have set in the ECM and what you manually set it at during the IAC & TPS adjustment. One thing that I try to achieve is minimum IAC to be able to run at idle.

Thanks again doc!

I worked on the car again tonight and here is what I tried...

*pulled and plugged small vacuum lines from back of HSR
*readjusted IAC minimum air
*pulled and plugged brake booster vacuum line
*capped other large vacuum barb fitting
*measured vacuum with gauge - fluctuates between 14 and 16"

I thought maybe my alternator wasn't keeping up (I have underdrive pullies). Here is what I found with that...

*I have a 105amp alternator
*at hot idle, 14.1-ish volts
*at hot idle with primary fan on, 13.4 volts
*at hot idle with primary fan, vent blower motor, and headlights all on, 13.1 volts
*car surged when i turned the headlights off and on with all the stuff above also running

Could the underdrive pulley on the alternator be causing this? If not, any ideas based on today's findings? I'm running out of things to check

Thanks guys!

What are the specs on that cam? duration at .05 lift and LSA

EDIT: I have never liked the idea of underdrive pulleys for the alternator!

Cam is a Comp Cams XFI 268... 218/224 with a 113 LSA. I believe the lift was .576/.570.

Thanks!

just swapped my HSR onto my new 383 which i just started a thread tonight on.

im running the XFI280 cam with 230/236. and ive had no idle issues...and thats with the stock 350 TPI chip! (just to see if shed run) these larger cams are gona require more idle RPM but a 200 rpm surge isnt too horrible.

id try the propane trick that is the easiest way to check. your TPS voltage should be around .5-.52 volts. check it with a scanner. IAC is no fun to play with... to adjust u need to push in and wiggle with ur thumb, dont just push in.

i have underdrive pullies on mine as well. but i have to take the alternator pulley off bc my charging was HORRIBLE! i left the crank on but i found a smaller than stock alt pully and threw that on. it helped but its by no means great at idle.

i kno its stupid to ask but did u mess up one of the plug wires? this is very easy to do. resort to manual for diagrams. i would make sure ur TPS is working right and set at .5volts... also make sure when u step on the gas and keep the pedal steady that the volt readings dont jump around (that means its bad) the readings should stay steady. check min voltage of .5volts with foot off gas in park, then check max voltage which should be 5Volts or close to it when the gas pedal is mashed.

why not just swap the stock pullies back on and see if it helps. check the MAF too by smacking it when the engines running to see if the idle changes, any changes means the MAF is bad. i hope u set TDC correctly and degreed the cam to TDC. and u didnt mess up on the distributer installation? id check to make sure TDC 0degrees is at the #1 plug on the distributer cap etc.

lastly i would blame the chip from TPIS. how much it cost u?

Thanks for the info customblackbird!

My understanding is the TPS is .54 stock and I bumped mine up to .58 at idle.

Maybe I did that wrong? From the tech guide, i jumpered the two connectors in the car, turned the key forward, waited a few seconds for the IAC to extend, then disconnected IAC, turned ignition off, removed two connector jumper, started car and set min air with torx screw. After set, turned car off, disconnected battery, plug in IAC, reconnect battery, and start motor.

As far as I know they are right but I will double check them using my Haynes manual!

I think that is a good idea and what I will try next.

I tried unplugging the MAF and it didn't help... car still surged. The MAF reading on the scanner shows 10 to 11. The guy at TPIS said that is high for a 355?

Honestly not sure... this engine was put together by a local builder.

I'm not positive but I remember the distributor was pointing toward #1 cylinder at TDC. If it's a tooth or so off, will that cause the idle issue? The distributor is a new one from Autozone.

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The original cost was $375 but they have done several reburns for free.

from what ive read the TPS is around .45 or something and bumping it to .5-.52 volts will increase throttle response. i kno mine was low like .45 set from the factory (when i bought it 5 yrs ago) id try lowering it to .5 to .52 volts. doesnt say what to set it at in the haynes manual that im looking at right now. but it does say intermitten voltage can cause fuel burts to disrubt idle etc.... check for jumping voltage.

IAC is on section 4B-6 in the haynes manual. you have no set the IAC correctly. the pintle must be no more than 1 1/8" from the tip to the back of the threads(by the body of the sensor) and if it is more it must be reduced. determine if type 1 or type 2 IAC and then adjust accordingly. 1st type says press with thumb and wiggle... 2nd type is to press with thumb and turn clockwise. THERE IS NO ADJUSTMENT OF THE IAC VALVE AFTER INSTALLATION... i have no idea what u did or who told u to do that.

unplugging the MAF will make it ALOT worse... wont correct the problem. the fact that the engine didnt try to kill itself with it disconnected is not a good sign. i dont kno about the 10-11 or watever i just kno it should read .5V at idle and 4.7V at wide open throttle. I said to smack it while connected and the car is idling bc if the MAF is bad it will then cause Idle change... if there is no change then the MAF is fine. dissconnecting it is not the correct way to diagnose this. dont wack it with a mallet... just give it a good sturdy hand tap. also if the MAF is bad u should be throwing a code or something... which im guessing ur not. dont forget to check the hot wire side of the MAF... relay that when the MAF is turned off it makes the sensor wire inside the MAF glow red hot to burn off any contaminants. if it doesnt burn it off then the MAF could be getting false readings due to buildup on the wire.

easy to check TDC... remove #1 spark plug and slowly rotate engine by hand (have someone do this while u keep ur finger in the spark plug hole) and watch as 0 degrees comes around it will either be the exhaust stroke or compression. if air is pushing ur finger out then its compression and its TDC... stop at 0 and leave. if not then u have to continue for a full turn. (have the distributer cap off and watch the inside cap to make sure its on the #1 spark plug terminal) mark the distributer for #1 before removing the cap. this will varify 0 degrees at TDC and that the distributer was installed correctly. being a tooth off on the distributer will cause HAIRY CAIRY on ur ignition timing etc... causes false ignition timing/detonation/miss fire etc not to mention being a bunch of degrees off on timing. when installing the distributer to get it correct u have to line up the distributer a few teeth off (before #1) the gears are slanted and the distributer will turn as it is pressed down. this is where it fools most ppl. Point is to verify the basics and start with a correct and known base.

also ur setting fuel pressure with vacume off correct? also low compression on the #1 cylinder is prob just a leak by the piston rings. if the builder had to gap the rings and he gapped the #1 just alil more it will cause a fluctuation like that. those compression readings seem low to me. esp on a 10:1 engine.

i ask about the chip bc i need to tune mine. but for the 375$ i could take it to a dyno and have it done that way.. just dont want to spend that kind of cash. most companies wont tune mine bc of my cam lol

Thanks again for all the info customblackbird!

So far, I took the throttle body apart and measured the IAC and it was within the 1 1/8" max limit. It was also clean as it is fairly new. I also checked the plug wires and made sure they were in the right order.

I spoke with TPIS today and they said that my idle fluctuating ~200rpm sounds normal and probably is just the way it is due to the high lift of my cam. Does that sound right? Or are they just trying to avoid further help?

Thanks!

Trying to avoid further help.

Is it a TPIS cam?

I'm wondering if its a tune issue. Stall saver could be kicking in as someone suggested. Do you have tuning abilities?

yes they are basically telling you, you have no idea what your talking about... corperate punks!! lift has nothing to do with idle....its all about lobe seperation and duration, im running the hot cam which is 218/228 on a 112 lobe seperation..i have no probs at all

Thanks guys! That's what I was thinking too.

gsf-87IROC, my cam is a Comp Cams XFI-268.... 218/224 w/ 5.76 intake and 5.70 exhaust with a 113 LSA.

Sorry but I'm not familiar with the Stall Saver. Is that something I can see on my scanner? I don't have tuning capabilities.

The stall saver is programmed into the Eprom chip. These are three levels, I had missed with my settings last march, and now cant remeber any details, But I know that its programmed into the Eprom chip. Has TPIS said anything about the stall saver as far as their chip is concerned?
Also, about your cam, its on the edge of having some lope. Its too late now, but if you ever get a new cam, do not go below a 114* LSA.

Thanks for the info doc! I will have to call TPIS and ask them about the stall saver. Is there really that much of a difference between a 113 and 114 LSA?

Even though my build is pretty new, I've been toying with the idea of getting a bigger cam like a XFI-280... a little less lift, more duration, and the same 113 lsa.

I have essentially the same combo (as the OP); my car idles smoothly with little fluctuation and slight lope. If everything mechanical is correct it must be the tune. Kevin91Z has mine tuned nicely. Only a few changes were needed to the part throttle section when I switched from modded TPI to HSR, although we recently discovered that 24# injectors do not flow enough fuel in the upper rpms.

With my 24#/hr injectors on my Accel SuperRam, I was running around 52 psi on the AFPR. Currently, I am running 44 psi with the HSR and 30#/hr injectors (remember I have a 395 cu.in engine in my beast)

The 113* LSA will lope a little bit, so I think that the un-steady idle is mostly due to the mechanical situation, as well as, the Eprom tune.

EDIT: removed comment concerning IAC position.

I am now in the same boat as u. I am running the XFI280... and its def got some lope to it!

its idling weird... i increased idle RPMvs coolant temp to like 850-900 and i cant get the IAC counts below 65-90 counts! it also is jumping around like 200-250rpms... goings up and down up and down. im also only getting like 15inches of vacume. i also have a hesitation in gear above 1500-2000 and it basically cuts out on me at like 2000 in gear and is surging all over the place.

whats the deal with this stall saver? i saw this in tunerpro and i didnt touch it. could this be the problem?

First off...the XFI 280 is a big cam...230/236, right? The low RPM manners is going to be tough, even in your 383(I am building a 383 and am opting for a 224/230 after talking to some people)...but you should be able to get it liveable. I had a 224/230 in a ZZ4 and it did OK around town, but forget it trying to drive below 1700 rpm or so...) Low vacuum...welcome to large cam world. That actually doesn't sound bad. If your brakes have problems, you may want to put a vacuum reservoir on it.

As for the IAC counts, you need to do the TPS adjustment procedure. You'll have to modify this some and do the best you can...this should get your IACs down. Bigger cams won't idle as low as what the factory procedure wants you to take the car.

As for stall saver, I usually adjust that with the minimum idle...put it about 200 below the lowest idle I have it set at...but I don't know if its necessary...I don't think anyone told me to do that, I just started doing it.

I'm also interested in how yours drives. I talked to Dan(WS6transam) and he said the powerband is up at 3k and up...feels great...but thought he'd go smaller so it was more fun crusing around town in...this was what made me settle on the 224/230 type cam. I'm 34 and my car is mainly used cruising to work and taking my daughter to daycare...so I want torque, good street manners...and at the end of the day, the dyno chart doesn't mean much to me other than bragging rights.

My XFI-268 surges about 250rpm or so... is that normal for a cam this size?

Thanks!

Back to the IAC minimum air and TPS setting:
With more cubes and bigger cam, I think that it is very important to complete the IAC and TPS adjust a little different than in our tech article. I want to get the minimum assist from the IAC so that the engine runs at the programmed idle RPM. For my situation, I have programmed the idle RPM (at full warm up) to be 850 RPM. Therefore, I set the minimum air RPM during the IAC adjustment to 750 RPM. After the IAC adjustment, I complete the TPS adjustment. It seems to me that my engine runs best when I set the TPS to 0.60mV at idle.

Big cams are going to have some surge, 150 RPM up and down (even 200 RPM) does not seems bad to me and is acceptable.

I hope this helps.

GFS, well yea the cam is by no means small but orr89rocZ got his tuned and his was like 230/246. so if he can do it i can. im pulling like 15in of vacume mostly in idle and its more than enough for my brakes. they work better than they ever have before! and this is a huge plus bc i couldnt even lockup the front wheels ever! i had replaced everything (brakes, but the hard lines) and never got more wheel lockup. ran new lines etc and new rotors/pads all way around and ditched those SUCKY A$$ stock disks for my ford 8.8 disks... no more "clatter" going over bumps etc and they are alil larger.

yea well i fixed the idle issue mostly. i got it to idle like 900-1000 in park, and idle only fluctuates like 100-150rpms... IAC counts are mostly 0 but it does fluctuate like 0-30 sometimes. I was running an older 02 sensor for engine breakin i replaced it with a new NKG that i had for after breakin.

i set the closed loop for the 104 temp and it does come on. not a 104 but up higher like the 170ish range. Im was running lean in open loop but then i added .5 to my MAF table1 and now im running rich in open loop(says autoxray) and my 02 gauge (narrow band) says im usually stochometric. once it goes into closed loop tho the gauge bounces around from lean to rich (kinda cool to see the gauge flutter from red LED to green LED lol) Autoxray also says rich/lean pretty fast.

timing comes in around 34-36 at idle! integrator is at 128. injector pulse 1.7/1.8ms at idle and goes to like 2.3ms while driving under load. MAF flow is 13-14g/sec at idle. but i have a pop in the exhaust when i stab the throttle in the 2000-3000 rpm range at idle?

I took it out for a drive to break in the trans, this thing is hesitating and surging and popping all over the place. AutoXray says im pulling 43-45 degrees of timing at about 2000 rpms and fluctuates naturally but this is ALOT at such a low RPM right? injector pulse shoots up to like 2.3ms as well. My dad has built many cars with Carbs and he says its got wayyy to much timing. 43/45 before or at 2000 is too much i think. havent taken the car above 3000 bc of new engein and trans only has 5miles on it so far.

SO what do i do? should i just start with a stock AUJL 63 bin which i have and then see what the timing does? the chips ive been trying were modded by Orr89rocZ. and he added a bunch of timing down lowww. I also reread my stock 350tpi memcal and motorvation strip chip... should i start with one of those? i like the AUJL bc i can edit more than my stocker and it has the cold start injector delete which i need for the HSR.

I usually start with a new chip when I redo an engine. Start with the popular 89 code if you're running MAF...whats that...was it ARAP? I can't remember.

doc...you and I are on the same page on the IAC/TPS reset.

blackbird...you want your IACs about 15 at idle I believe...maybe in Park with an auto. Not sure.

Its been 3 or 4 yrs since I thought about tuning much...so I'm probably not the best to be giving in depth tuning advice...as things vary and I may be far behind in my knowledge.

The timing does sound high though...Definitely at least take your timing back to stock levels...use the 89 Vette code. I'd never use another persons timing tables...timing will kill your engine. You should start with your own and go from there.

250 rpm surge from the xfi 268 is excessive. My cam was 230/245 on a 109 lsa with over .600 lift and surge/hunting wasnt over 200. Probly below 130 rpms most days and I didnt even try too hard to get it stable. To get it more stable you really need to focus on your fuel delivery and if your battery voltage is varying abit due to accessories sucking power or underdrive pullies, then you need to adjust your injector offset vs batt voltage tables.

89 Vette ARAP code has high timing, higher than my table. My table has 40 as the max value at looow LV8's and high RPM but PE mode if enabled will want to add another 8 degree above 4800 but while driving that will never happen. Plus I have max spark advance option set to 44 degree anyway so it shouldnt be seeing higher than that.

Formula Novice; I dont think idling at 10-13 gm/sec is too high for a 355 but my 383 was around 14-15 sometimes near 16 or so, and was abit more aggressive than your 355 build. Stock TPI 350 wasnt below 10 I dont think... but a decent cammed setup should see around that.

Its probly surging abit due to abit too much fuel and possible timing changes in between LV8 cells. I found you need to lock timing at idle in all cells around where you idle and then tweak MAF table 1 for idling fuel. I dont believe i had to play with idle stall saver stuff on my car, i remember trying breifly but i got it to somewhat stabilize after tweaking the timing and fueling.

Formula, i dont think you'll need to adjust stall saver or injector pulsewidth offset since your using 24 lb injectors and stock 350 tunes are 22lbs so they should be very very close. It soundslike some minor tweaking of the fueling and timing will be necessary to stablize that idle if you tried everything else and they didnt work

Oh yah...forgot about that time spark table down around idle! When I first started playing with a heavily cammed car...the spark table is so damn flaky down at idle...you have to level out your timing close to idle. Totally spaced that until I read that post. Its been a long time.

Factory MAF timing tables are all over the place...somewhere I 'think' I have an excel spreadsheet that levels everything out...at least I HOPE I still have it and laptop crashes didn't toast it...it sure was handy!

you have jumpy spark at idle along with variance in fuel delivery, you will have unhappy idle.

Thanks for the info guys! Sounds like I may be investing in some chip-burning tools.

Just curious (i'm still learning about cams), is it the cam lift that is causing the issue? I thought the idle was based more on LSA than lift or duration?

Combination of the 3 but overlap which is directly related to LSA will have influence on how much fresh air gets blown out the exhaust. High overlap cams which are the big duration cams on tighter lsa's will have intake valve and exhaust valve open at the same time longer, so while exhaust is going out, some intake charge gets sucked out too, resulting in the computer seeing more air in exhaust..thinking its lean when really it may not be so in the chamber. you can tweak your o2 sensor parameters in the code to correct for this somewhat. I've played with them before and have gotten my BLM's to show near 128 at idle when stock it showed 160 which was lean. Not an expert on it tho, i just ended up turning closed loop off and working open loop only. I found it easier for me

Thanks Orr89RocZ!

So, even though the XFI-280 has less lift than my 268, it may idle the same or worse since it has more duration (FYI - same LSA)?

What's weird is my BLM's are around 128 already, so it doesn't seem like it's too rich or lean.

I believe the "intake charge gets sucked out" you were describing is what TPIS was telling me. They said something about the velocity of air in the combustion chamber and, even though everything was mechanically & ECU ok, it may be resulting in a small vacuum leak due to the high lift? Not sure if that makes sense at all... again I'm still learning about cams

280 has more duration and thus more overlap even tho it has same LSA. it will have a rougher idle than the 268

Great thread. I am in the process of choosing a larger cam for my zz4 and have picked up alot of good general information from the responses to the OP.

Keep in mind as you review this thread whether we were discussing 350s or 383s. The cam size choice between the two would be different.

I was reading on another forum that between a 350 and a 383, if you add about 10^ of duration and subtract 2^ of overlap, you'll have the same basic mannerisms of cam as you would in the smaller engine. I don't know the truth of that statement, but I think it was on Hotrodders.com and I don't see many kids that sound like 12 yr olds posting over there.

Anyway, so that would imply that the 'rule of thumb' is that a 211/219 cam(I'm running in my 350 and love btw puts 310 to the ground with a nice flat torque curve. Topped off by a HSR and AFR 190s)...if you add 10^ to it a 221/229 cam would be about the same mannerisms in a 350. Mine is currently on a 112 LSA and I guess what that means is a 110 LSA 221/229 cam would give me the same thing.

I'll defer to others on advertised duration vs duration @.050...I'm not versed enough in cams to digest that.

I've run a GM846(222/230) cam in a ZZ4 and while it pulled to 6500, it didn't feel very good until about 3k RPM and with my 3.42s, I couldn't use 6th gear at 60 mph. That 211/219 cam will chug along at about 1300 rpm 'ok' but is very happy to pull the car down the road at 60 mph at 1500 rpm in 6th.

After reading that I've pretty much settled on a 224/230 Xtreme Energy Cam although I'm debating a 219/228 Voodoo Lunati cam...mainly due to the name! Yah, I'm stupid. Anyway, just be careful when reading about cams you pay attention to the cubic inches that are discussed.