About a month ago the car started just dying suddenly. No coughs, splutters or backfires. I changed the fuel filter, plugs and wires. Things only got worse. Here is what happens.

(91 Camaro RS, V6, Digital EGR, owned about 4 months)

Start cold, car idles fines.
After about 30-60 seconds the engine will shudder, miss and almost die.
It picks back up but starts idling real high.
I tap the gas pedal a few times but no drop or change.
I turn the engine off and restart.
Now the engine idle is more normal.
The engine runs but there is a definite up and down pattern to the idle.
I can take the car for a drive but I have to keep the idle up or it will die.
During the drive the engine will just die with no warning.
It can be restarted most of the time but runs rough.

Today I changed the dist. cap, rotor, ign module and coil. I also checked the PCV valve. No change. Short of taking it to the dealer for diagnoses I don't know which way to turn. It does not seem to be fuel or ignition related based on symptons. No backfires, burp, or loss of electrical have me stumped.

Thanks for any suggestions.

 

tps or iac going south?

 

Sounds like a vaccum leak..try pluggin the brake booster to isolate it and see if it changes (idle) can drive it too but pedal will be hard to push and be careful.Also you can start the engine and just press the brake and hold it and notice the idle if it gets crazy or the engine dies...let up and if the idle changes with the pedal pressed or depressed booster is leakin.

 

I visually checked for cracked or disconnected vaccum hoses and I did the brake pedal depress per above suggestion with no change.

If I connect a diagnostic tester will a bad TPS or IAC sensor show an error code? The local dealer is the only one around here with a tester that will connect to my car and they want $75 to do it. If there will be no error codes then I would be wasting that money.

Are the TPS and IAC sensors hard to change?

 

Have you done any sort of checking the MAP sensor? That's about the only thing left you have to check. Also, try cleaning your IAC...

 

Thanks for the input fellas. I am pretty old school so all the sensor thingies are lost on me. The wife and I decided to let the experts diagnose the problem and we will go from there. When I know what the cause is I will post the results so others can be helped by it. Onward and upward, right?

 

get some codes and look it up in your book. I would also check your maf sensor. just disconnect it to see if it runs properly. does your engine light come on?

 

The car was delivered (barely) to the dealer for diagnoses. The check engine light never came on during the whole process. I am very curious about what they find.

 

Hey PopCycl, what did the dealer tell you?

I think the IAC motor may be bad, it's "hunting" for an idle, and it may stick open, letting in too much air and killing it.

 

91 did not use a MAF sensor. I know my 92 does not have one. These cars are speed density from 90 - 92, aren't they? Please correct me if I am wrong. Definately want to know the outcome of this one. When I had a similar problem I found two things... first the bore that the IAC seats into was loaded with gunk. the head of the IAC valve was sticking to it and had to struggle to retract. Car stumbled every time I slowed to a stop especially in the warmer weather. The other problem I tracked down was 2 vacuum leaks. One at the climate control head, the slider that controlled the vacuum solenoid for the vent flapper doors had a broken tab. The other leak was at the AIR pump. I do not know if it is the pump itself or the vacuum line. Hard to reach, so I just plugged it at the TEE that feeds the FPR and the pump, for now. Keep us posted!!!