Hi Guys, I posted this in the ECM forum too, but thought I'd get more info here. Sorry this is a little long...
I need a little help interpreting a problem with my 1992 Camaro RS. It's a 305/auto car. I've converted it to TPI unsing parts from a running 92 Z28. It runs pretty good until it warms up.
Once it reaches operating temperature, its starts to idle erratically. The problem is most pronounced while stopped at a traffic light. The engine will nearly stall, surge to recover, and eventually will stall. Putting it in neutral or giving it a little gas helps. The car drives down the road with no issues.
It's throwing code 13 and code 42. The code 13 has been addressed with the installation of a heated O2 sensor, but that didn't help the idle issues. The code 42 is what I don't get. The dizzy, module, cap, coil, rotor, plugs, and wires are all new. Maybe the code is only there because I've recently set the base timing.
I was able to hook the car up to a friend's data-logging program The other day. At idle, the timing advance is just jumping all over the place, from 9* to 24*. When you drive the car, it evens out and holds steady.
When cold, it runs perfect. I should mention a lot of people thought it might be a vacuum leak or bad coolant temp sensor. I've checked all vacuum hoses and find no leaks. I've gone as far as replacing the intake gaskets and coolant temp sensor, no effects.
Thanks for any advice.
Dave

 

In my experience, the most common causes of idle surging are a dirty/bad IAC sensor, vacuum leak, failing fuel injectors, or a failing fuel pump.

I would start by removing the IAC and making sure it is clean and the spring is "springy" (not real compressed). If that isn't the cause, get a fuel pressure gauge and verify the pressure is correct and steady. Beyond that, ohm the injectors and continue checking for vacuum leaks.

Hope this helps!

 

I had this exact same problem and somthing I did helped out a lot, but she still kinda does it sumtimes, but not bad. If you search under my name you might find it. I forget what I did. I do know I put a new IAC in. Changed 02 sensor.

 

IAC has been swapped with a known good one (from a friend's car), and I've cleaned the IAC passages in the throttle body. It's not the issue.
It pulls about 21" vacuum at idle.
Fuel pressure is steady 39psi.
I've plugged all vacuum ports and run the engine with no improvement. I've replaced the intake gaskets and again, no change.
I ohmed the injectors and they were all within spec.

I really feel this is ignition related. A data log clearly shows erratic spark advance at idle, and I'm throwing a code 42 "Electronic Spark Timing (EST) Circuit". It might just be there because I recently set the base timing (straight up).
This problem came up after something caused the coil and ignition module to fail. The car ran fine before, but ever since replacing the coil and ignition module, it's done this. I've tried other coils and other modules, still no changes.

 

Hi Big Dave, GM issued a TSB for a worn distributor shaft that can cause erratic timing. But a new dist kinda eliminates that. Be aware also that erratic idle will cause erratic timing as one follows the other. Even though you cleaned IAC passages, that doesnt eliminate a faulty IAC solenoid. Do you have a scanner? If so try "IAC test" under "System tests" it should allow to control IAC from minimum idle to 2,000 rpm. If the IAC doesnt respond or is slow responding it may be bad. Also check MAP sensor voltage and TPS as these are main inputs for fuel control. Though you should have eliminated the O2 by replacing it, be sure to watch that as well. Ive had them be bad out of the box.

 

Have you tried clearing the code to see if it comes right back? If it does, the SPOUT line may be shorted. Double check the 4 pin connector at the module for pushed out terminals. Check the harness for shorts. Did you test the pick up coil? If the code doesnt return, the most common cause of erratic idle is lean fuel mixture. Again, scan ECM data and look for potential causes of a lean condition.

 

I've checked the harness for shorts, found none. The new dist. I installed included a new pickup and module, nevertheless, I did verify a good signal from the new pickup before I installed it. The module tests good, and I've tried a few known good ones (again, from friends' cars) with no changes.
I don't have a scanner. I borrowed a friend's laptop and ALDL cable to do a data log. The problem could be in my interpretation, but everything I see points toward the ignition. Again, I may not be interpreting it correctly. Frankly, I'd love it if someone else could have a look at it.
I don't have a scanner. What kind do I need to be able to perform the IAC test?
I've checked the TPS. I don't recall the values, but it swept smooth from idle to wot. What should my MAP voltage be? I'll check that as well.
Thanks a lot for your help!!!

Dave

 

I just took another look at my data log.
TPS is .57v at idle, 4.18 at WOT.
MAP is reading about 36kPa, no mention of the voltage.