I have a 92 STS that runs good, however sometimes when I stop at a light, it stalls. it starts right back up, but I'm wondering what would cause this. I had it checked, and thought it might need a tuneup, but the mechanic said that might not be the case. Any other reasons for this happening? Thx in advance.
I was having a similar problem with my dads 99 grand prix it's rpms would fluctuate up and down and it hatted stop and go traffic and every so often it would stall. So we took it to the shop and they did some thing with the computer replaced a sensor or something. I would recomend having the shop diagnose the problem (probably gonna coast about $280-$315) and you can always spend about 1.75 for a new PCV valve that could also be your problem.
Probably the ignition control module or hall effect (cam position) sensor. If it stalls suddenly, this is the case. If it stalls because the engine load suddenly increases due to an engaging A/C compressor, it's the ISC motor.
If the engine idles at an abnormally slow speed (<500rpm), the ISC may be stuck in a retracted position. Test the ISC under the hood by opening the throttle by hand...the ISC should extend...let the throttle go and the ISC should retract allowing the engine to return to a normal idles speed. Monitor the idle speed digitally via PD11 in the PCM diagnostics.
If the engine idles at a normal speed around 600rpm, then it is likely a bad ICM or hall effect as Huf indicated. ICM = $21 @ AutoZone. AutoZone can test the ICM, but the test may result in a false pass since the ICM may only fail in the higher temperature conditions experienced when installed in the distributor.