My z28 will idle at 500 cold and once fully warmed sit at 700ish. This is backwards isn’t it? Shouldn’t my idle be higher when cold and lower when warm?

 

PCM controls the idle RPM, along with the cold start A/F ratio, based on coolant temperature. RPM vs. temperature is dependent on transmission type. Is your trans auto or manual? The PCM attempts to maintain the idle using the idle air control valve (IAC).

There's a stock programming table of idle RPM vs. coolant temperature in my LT1 scanning guide:

https://www.camaroz28.com/forums/com...-guide-886891/

 

I have the manual transmission

 

It should be idling at 800 RPM fully warmed up. Do you have a way to read data from the PCM. You need to see what the IAC counts are reading if it idles at 500 RPM. That will take a program like Scan9495. Free download, just buy a cable:

https://www.camaroz28.com/forums/com...95-lt1-874306/

If the PCM is commanding the IAC to open up to an increasing number of counts, and RPM is not increasing, could be a faulty IAC, The maximum counts are 160. That would be the PCM telling the IAC to open to the maximum possible. But there is no feedback as to what position the IAC has taken. Could be faulty IAC, excessive build up on the pintle.

IAC Electrical check:

http://shbox.com/1/iac2.jpg

Resetting IAC usually doesn’t help, but worth a try:

4th Gen LT1 F-body Tech Articles

Is the idle smooth, or is it struggling and unstable?

http://shbox.com/1/iac3.jpg

 

Do you have a link to a reliable cable? I want to try tuning a few things as well so I would like a really high quality cable. Would the homemade one be that reliable?

 

I unplugged and replugged the iac several times with the engine running with no difference at all. So I’m gonna replace it later today.

 

That is an unreliable test. You should check to see if there is any cleaning needed and maybe do a reset afterward.

4th Gen LT1 F-body Tech Articles

 

^^^^ THIS ^^^^

Unplugging it proves nothing. Don't get caught up in playing “parts replacement roulette”…. expensive way to solve a problem, usually not productive.

 

I replaced it and 1 I saw excessive buildup and possibly oil behind the throttle blades and all in the intake manifold. Do you guys know what this could mean? 2, my car now starts idle at 2k slowly drops to 1k and stays there which is too high. Do I need to reset the pcm and relearn idle?

 

Oil buildup in the throttle body and intake manifold can be a sign of a dirty PCV valve, or excessive piston ring blowby.

If pressure builds up in the crankcase and can’t escape through the PCV valve, it is relieved by flow reversing through the hose from the throttle body to the passenger side valve cover. Normally filtered air flows from the throttle body to the valve cover, where it is pulled through the crankcase by vacuum through the PCV valve. But when it’s relieving pressure buildup from ring blowby in the crankcase, it picks up oil mist and carries it into a chamber on top of the throttle body (directly under the cover plate). Then it drips down in front of the throttle blades and gets carried into the intake manifold.

 

Ok sweet thank you I will check the valve also do you know the right method for pcm reset, idle relearn?

 

What if I didn’t set pintle length? Will the computer adjust it self or do I have to take it back off?

 

I gave you the link to the IAC reset procedure in post #7.

 

Yes but I’m curious I did not set the pintle length. Will the pcm not set it self? Do I have to re pull it and set it?

 

It starts at 1900 and idles down to 1000 even when warmed up