I have a 1995 C1500 with a 5.7 and TBI Fuel Injection. The idle is pretty rough and sometimes it gets very close to stalling. I have replaced almost all the Sensors, Plugs, Wires, Distrbutor Cap. It seems like when I turn The Air Conditioner on, it idles better. Anybody have any ideas on why it idles like this? It is not throwing any codes.

 

Our 93 did this especially at cold start. Mechanic found it needed a new distributor. Ran great and much better mileage after replacement.

 

Mine seems to run better Cold and gets worse as it warms up.

 

what are the idling RPMs respectively?
as your car warms up, it will idle at a lower RPM, so there's that to consider (could be playing a part)
Have you checked for vacuum leaks? also clean out the throttle body.

 

and im assuming you already replaced the idle air controller?
doesn't sound like a misfire sense you are getting no codes.

 

Checked for Vacuum leaks, Replaced IAC valve twice, Replaced almost all sensors, I am leaning towards Distributor, but Distributor was vreplaced a couple years ago, but replacement was a cheapy, Car does idle better with AC on, Anybody know why it would do that? Same RPMs? I would call it a Lope in the idle.. Not real consistant. Throttle body was replaced with a rebuilt one a couple years ago, Not totally ruling that out.

 

I just like to list out my thoughts:
When in idle your car runs rough, but better with the A/C is on. I am now going to assume that it is running better because having the A/C increases the load on the engine. with this assumption, having your heater on should also increase the load.


Leaves me with two thoughts:
either...
1. There is something with the ECM.
or
2. The timing is out of whack.

 

Exploring #1, and hoping your ECM is fine,
When you replaced the IAC, did you perform a reload procedure?
simply remove the ECM fuse(s) and reinstall
this will clear all engine codes and allow for a new IAC relearn procedure.






Exploring #2, you can try to mess with timing by adjusting your distributor. (or the distributor is bad).


Try #1 first and hope for the best.

 

Can you please explain the Relearn Procedure? Every time I have looked it up, I always find differant procedures.

 

the reason they all vary is because it should learn it on it's own.
the universal GM process: (should work)
Disconnect the Negative cable for a few minutes (I prefer to remove ECM fuse since resetting the Codes is the desired result anyways). While The negative cable is dissconnected, pump the brake pedal a few times to clear out any voltage in the system. Re-connect the negative cable after this is complete. Turn off air conditioning controls and all other accessories.
Run the engine up to operating temperature and shut off.
Apply the parking brake. Start the vehicle and place it in drive (A/T), or neutral (manual).
Run the engine until the cooling fan has cycled on and off, or for a maximum of 10 minutes.
Turn the ignition key off for at least 5 seconds.
Restart the engine and again shift into drive or neutral. Allow engine to run for at least 5 minutes.
Shut off engine for 10 seconds and restart.