'94 V6 3.1 Idling Rough

I have a chevy cavalier v6 3.1 mfi. The car has a tendency to idle rough and bounce back and forth between 600 rpm and 700. I was idling at a redlight today with the heater going and I recieved a check engine light briefly, which then shut off after about a second. Shorty after that, the engine shut off. I put it into park and restarted with no problem.

My bet is the Idle Air Control valve, any other suggestions? Thanks.

Note: It doesn't do it in park.

Update: I got tired of stalling in traffic for the second time, so I took some advice and put fuel injector cleaner in. Now:

1. My speedometer doesn't work
2. Check engine light is on
3. I need not push on accelerator to reach 30 mph
4. RPMS are either extremely high or extremely low

The IAC motor would be a likely suspect for the rapid change in RPM's, but is it the IAC that is to fault or some input to your ECM or the ECM itself that is causing the rapid RPM change. I would try just retrieving the codes that are stored in your ECM and go from there.

The IAC motor would be a likely suspect for the rapid change in RPM's, but is it the IAC that is to fault or some input to your ECM or the ECM itself that is causing the rapid RPM change. I would try just retrieving the codes that are stored in your ECM and go from there.

I think you're right about the ECM might being bad. I drove it today and had short grinding noise for about a second during startup and then my ABS and emergency brake lights came on. Brakes work fine though so I'm starting to think its the computer. I'll get it tested first. This out to be fun.

Scratch what I said. Now it's stalling for no reason whatsoever. RPMs were fine this time, but I was driving in rush hour traffic on the busiest road in town and the car stalled at a red light. Right before it stalled I noticed the throttle wasn't responding like it should (it took a second to respond to the gas pedal accelerating). Even before this I had started my car up after picking someone up and the park idle was extremely high (past 2500) and rising. I shifted before it had a chance to redline. Is this possibly a faulty TPS?

Three things I can think of. The first and maybe least likely is a bad temperature sensor. This will cause your ECM to send the wrong amount of fuel to the engine for some reason. You can check this with a volt meter.

Second might be your vacuum lines. Whenever you have something wrong with your idle this is a good place to start. Not to mention it is easy to check. They run underneath your upper plenum and you can usually see if one has come off or at least give it enough of a push to close it up so the problem can be isolated.

Last thing would be your TPS. Again this is something you can check with a volt meter to make sure it's within range and sending the proper signal.

Im thinking PCV valve or tps. Any body think this also?

check fuel pressure and volume. also injectors are known to go bad and take down the circuit.