I hope i dont loose any one and i know this is kind of long but i wanted to be detailed in order for you to understand me....Im new to this....

Ok so i have this problem i have been trying to fix. Its getting on my last nerve.... Took my car to get dyno tuned. Everything worked much better after that, except the car would idle really low and would sometimes hesitate a little taking off and then it would kick in and take off perfect. It did it before it got tuned and i thought the tune would fix that problem. But it is still there. Symptoms are that everytime i shifted between drive and reverse it would bog down the rpms and raise back up ,but at times it would just die out. So i would have to turn the car back on and try it once again. It was irritating.

So i took it back to the dyno place and i was told that the IAC might need adjustment. So he hooked up to his laptop, and in about 10 min. he then bumped up the idle and messed around with the IAC to command it to give it more air (just repeating what he told me). Turned on the car and shifted between gears and again the car would bog down but now quickly raise the rpms without shutting off. So with adjusting the idle and the IAC it made the IAC force more air in to keep the car on i guess? The car idled fine in park and neutral. Stays around 900rpm, but around 850 ish 900 in drive. Is that normal?

Ok so i left the place once again and i noticed that when i arrived to a stop or a light, the car would stay idling around 850 ish to 900 rpm like i said and you can hear the cold air intake sucking air and it would forced the car to go and fighting me..As soon as i let off the brake the car would just accelerate on its own and pick up speed. ....

So i called the guy back and explained what as going on, he told me that these PCM's , there is only so much the tuning can do especially when adjusting IAC....The only thing he could do was adjust it again and adjust the IAC to give it a little less air then what he had set it for....

So before going back to him i decided to go through a detailed inspection of the car. I checkd for vaccum leaks and found none. Hoses were all fine. I decided to change out the IAC and the TPS all brand new to see if it helped. Put all new gaskets on the throttle body as well.

Turned on the car and the idle shot up to like 3000rpms and slowly started to come down but stayed around 2500 so i quickly shut it off. .... I dont know what happend. SO i started messing around with the stop screw on the throttle body and screwed it all in until the butterflies were pretty much closed.

I then turned the car back on, idle went up to about 1500 and slowly came down until it sat at around 900 and stays idling there. But now the car is back to doing what it was doing before i took it to get adjusted. BUT, now in drive at the light it idles at around 750ish and stays there. Note ( i go by what my auto tach tells me since my dash rpm gauge doesnt seem accurate at all.

Any how, I was thinking about adjusting the screw again and unscrew it out some more to open up the butterflies a little until it fixed the problem, but i figured the sensors would have fixed all this.....

Before i unscrew the screw back out again and take it in. What do you guys reccommend? any help i can get is appreciated. IM just out of ideas i dont know... I just cant get the stupid car to run perfect, Or maybe this is normal and im just worrying for now reason. Im frustrated...
Can anyone tell me if this is normal? because it has a cam and what not and obviosly its not going to perform smoothly as a stock car would....

 

With the hotcam kit your car should idle perfectly. If it doesn't then something is wrong. It sounds to me like there could be an intake leak or a vacuum leak. I know you said you checked but....check it again. This time with the engine running take a can of brake cleaner/starting fluid/anything flammable in an aerosol can and spray it all around the intake and vacuum fittings. If your engine suddenly idles up or down you found the leak. Also, do you have a scanner? hook up the scanner and monitor your IAC count, should be 30ish or so if everything is ok. If its unstable or really high that would indicate a mechanical problem again. Are you running a stock throttle body? Aftermarket ones take some mods to make em work right.

 

Idle speed should only be controlled by the PCM (IAC) not by the TB stop screw. Procedure is to open the TB just a little to let a small amount of air in then. Adjust the stop screw and make sure you get the TPS voltage at TPS=0% less than .75V or it will mess up the PCM control during stops. I run .71 V with my setup using stock heads and bottom end. This ends with an IAC or 59 in D at 750 RPM and a count of 34 in P/N at 800 RPM. Your Closed TPS timing should be in the 28-31 range for 400-1000 RPM. If this doesn't give a smother/drivable idle then you have other problems as per previous post. As LearJet asked in post #2 is your TB and MAF stock ?

 

Stupid question? Could his DFCO be kicking in between shifts? Thats what I would check, what those settings are at. Just my .02

 

well, throttle body is a 52mm. It looks like it was a stock one bored out, you know like those that they sell on ebay.....and MAF is stock as well. it still has the screen on it as well.

And i dont have a scanner or anything like that to check any data from the pcm...(*sighs*)

I unscrewed the screw on the TB again and now the car idles at around 950-1000rpm.. and in between shifts, it still bogs but not as much and doesnt want to shut off.... and the idle stays around 800ish in drive and both reverse...

The only bad thing about it is that you know how at start up, the cars usually idle high and slowly come down to the set rpm?..
Well before it would go up to like 1400 ish.

Now it goes all the way up to like 1900 ish at start up and in between shifts around 1600 ish.

(*sighs*)....just when i thought one thing gets a bit better ,the other gets worse.......

 

Its probably always going to bog somewhat between park and rev or drive with a cam in it and no stall. That is just the nature of the beast.

It sounds like you finally have the screw in a place where the iac is working ok.

You should have the programming set to idle around 950 in park and about 775 or 800 in gear. This is important to help minimize the bogging going into gear, basically you use energy stored in the crank to give the iac time to adjust to the sudden increase in load. Your start up and reving to 1900 and also slowly coming back to idle has to do with two things. The first thing is the closed tps spark advanced at the higher rpms sometimes you have to make the 1600 timing match or be within two degrees of the 400-800-1200 rpm closed tps timing. The second thing is the idle overspeed spark retard vs rpm needs to be very agressive starting about 100rpm above commanded idle rpm should cause about 6-8 degrees of retard working up to about 14-16 degrees of retard by 200rpm above commanded. That will bring your idle down much more quickly after startup. The high idle at startup is a combination of iac and timing. You can also get more aggressive with the idle underspeed table in order to keep the car from bogging quite as bad and certainly to keep it from stalling completely.

You had a vacuum leak after cleaning the tb when the idle rpm went up and hung around 2500-3000rpm.

What plugs are you running in it, as that can have a surprising amount of effect with this issue. I would recommend ngk tr5 plugs for something like you have.

No offense to your tuner really but it kind of seems like he needs to buy a clue. These are all very common issues with a4 cars with cams, sometimes even stalled cars do this to some degree.

 

Hmmm im not sure if i had a vaccum leak. Everything was on really tight with the new gaskets. I sprayed carbon choke cleaner all around and the idle didnt change wich indicated no leaks.... But messing around with the TB screw helped the start up idle minimize but it still seems high to me.. Almost goes up to like 2000 rpms and slowly comes down and idles fine... This started after i put the new TPS and IAC in....

I just did a tune up recently... Put in the AC delco plugs... I was told those are fine...

And dont worry.. I wish my tuner could help me out more. Im sure its something simple that he can retune with his laptop...

But i wanted your guys feedback before i go to him again

Last time i spoke to him he said he could lower the AIR back down coming through the IAC to see if that helps... but he went on telling me that with these old computers there is only so much you can do....

 

Print my post and hand it to him. If he is worth a damn it will be enough for him to get it sorted.

For the problem with feeling like its pulling at a light you will either have to lower the idle to 800 or below, or adjust the iac vs mph throttle follower tables for the bit about picking up speed just by letting off the brakes.

 

Hey WS6 Terror:

thanks for helping me out, i really appreciatte... i knew subscribing to this page would help...

I will definately print it out and pass it on to him.... I am probably gonna go up there next friday though......and i will update you on this ...

I hope he can fix my problem...

Now another little problem i noticed as well (SOMETIMES) only,,, why does it make this POP sound through the cold air when i smash the gas pedal sometimes.. ? every once in a blue moon when its cold or hot....

it almost seems like a backfire but does it for like a split second and quickly takes off like a beast.....

I doubt its due to the ignition since its runs strong all the time...

If you could give me any suggestions so i can pass it on to him as well. I appreciate your help...

 

Its due to a lean spike ie not enough transition fuel. There are certain ways to help it but then I'm not looking at your tune so I can't speculate about what has been done or why exactly it would do it usually its a bunch of little things. Most lt1's will exhibit this to some degree and you cant ever get rid of it entirely with a run of the mill street tune.

 

WS6T3RROR is right on when he says lean spike cause of not enough transition fuel.

Thing with the LT1 one of the things we all wanted all this time was control of the "accel shot" aka transition fuel. Well, I ran another trail on the stock PCM to test IAT/MAT vs Injector pulse to prove out some IAT vs fuel related things and found no matter what pattern of THROTTLE rate (0 to 100%, 25-100%, , etc), with a set VE/MAP number was injector pulse remained exactly the same, Meaning there was no short pulse of fuel/injector pulse increase when you slam the throttle to the floor (absolutely no change in injector pulse when throttle is jammed from 0-100%, 25-100%, etc) with constant MAP VE numbers, meaning the PCM must "know" how much fuel to add during a MAP/VE transition based of "jump" of the VE cells.

If "Accel Shot" was acutally an independant variable, then it would change pulse of the injector during a rapid TPS change. Maybe one more setting we can try to blame the folks at GM for trying to make easier, or maybe them just trying not to waste fuel, because we can simply lower injector constant to increase "pump shot".

 

HEY ws6T3RROR.... THANKS ALOT FOR HELPING ME OUT... Printed out your post and took it to the tuner.. PROBLEM fixed!.... Doesnt idle high on start up. It only goes up to like 1300-1400 RPM. Also Now when i let off the gas pedal it accelerates slowly and stays around 10-13 mph. I guess that is normal?. Well Atleast i dont have to fight with it anymore at the stops or lights...

 

Glad you got it all sorted out. Seems like some of us can do a little more with these old pcm's than others .

Picking up speed like that is pretty normal.