95silverbullet

Ok so i posted this in the "Fuel and ignition" section but i havent had much luck...

Ok so heres my problem..

I took my car to get dyno tuned and after that i noticed that the car would idle low and shake or surge at the light. It would idle in drive around 550ish or so..... And in park it would idle around 750-800 ish..... It did the same thing before i ever got it tuned but it wasnt as bad as after the tune and i figured it would go away after the tune.... Well. it was still there. I thought it was normal since it was cammed. The bad thing about it was that when i gave it gas it would stumble for a second and then correct its self and take off....But i was still not happy because at one point when i was reversing to park it shut off on me.....

So... i called up the guy at the place and he told me that the tables and something about the IAC needed to be adjusted, bump the idle and some timing.. So ok, i took it back and it took him about 10 minutes with his laptop and he was done. He then started the car and then the idle went up to 1100 in park and when he shifted into drive it the rpm's stumbled to like 500ish and quickly shoot up to 900 ish and sits at 1000 rpm's. Same goes for reverse.

So i hopped in the car and left. But after driving it for a while i figured it was still not right.... It just idles tooo high i think.Plus if i let go of the gas pedal it accelerates itself.... I already messed with the little screw in the throttle body and closed it almost all the way and no change so i put it back where it was...

I heard they should idle around 700ish-850ish in drive and around 800ish in park or soo....Now im just frustrated because i dont know what is going on.. I figured it was my IAC or something but someone in my other post told me that it was all in the tuning...

So i emailed the guy at the dyno place about it and explained how it stumbled in between gears and how it idled in drive... And this is what his response was:

"The little stumble when first shifting into gears isn't uncommon a lot of cars do it. Think of it this way, in park and nuetral the motor has no load, it's basically free spinning, then when you put it into gear, the load increases, this causes the idle to dip a little bit, the computer reacts by increasing the timing, and adding more air into the IAC. Since the computer cannot anticipate when you're going to do it, it is merely reacting to what yours did.

Adding the the air to the base idle table is what makes the car seem to pull away on it's own. You can try to close that little screw on the throttle body to make it better, although with these older computers, there's not much you can do in that regard. I can increase air, or decrease it. With the newer computers, there's a lot more control you can have with the little IAC valve"


So IF any one can help me out...I already checked for LEAKS and there is none....

Everything is working awesome on this car. Its just that idle that bothers me because i cant even hear my cam lopey anymore.. and its frustrating to try and fight the car at the light because it just wants to go on me......

Injuneer

Really sounds like the tuner is not familiar with "these older computers" You can't adjust the idle correctly with the throttle stop screw. You need to adjust it with the PCM. There are idle compensations in the PCM for sudden changes in throttle position, closing throttle shifts, decelleration, etc. Sounds like your IAC isn't responding correctly. Did he test the IAC valve? Have you tested the IAC valve?

This isn't really "Advanced Tech". I think you would be better off posting in "Computer...." or "LT1 Based Engine Tech".

cusz28

whats your fuel pressure at? that off idle stumble could be the lack of Tau caused by the low fuel pressure. that was always the classic signs of a bad fuel pump on my stuff.

Injuneer

No need to keep this open on the wrong forum. He reposted on "Computer Diagnostics and Programming", and got his answer - problem solved. Tuner apparently had failed to address transition fuelling in the PCM tune.

https://www.camaroz28.com/forums/sho...d.php?t=717316