Stalling at idle sometimes

[lt1redz]

I have a 93 Z auto. It is stalling at times like at a red light. It doesn't do it all the time. It has been doing this for about 2 weeks or so. After I restart it it stumbles then finally revs up. Last night the Mrs.couldn"t get restarted until it cooled down. It is not running hot only average temp on the gauge. For a while I have smelled gas on cold start. None after warm up.

I pulled the codes after the check light can on for about 10 secs. First code was 15 according to Haynes coolant sensor circuit low temp.The second code was 28 Transmission range circuit. Since this is a 93 and has the 4L60 not the 4L60E I'm lost...

Don't remember the check engine light coming on for the first code,but it could have happened to the Mrs. She hardly looks at the fuel gauge let alone any other lights that come on.

Could really use some help as this is my only auto.Thanks in advance..

[Joe 1320]

I would suggest looking into the IAC. The Idle Air Control valve is directly responsible for metereing additional air into the engine when the throttle blades are closed as in at idle or slowing down for a red light. It is possible for the valve to become carbon fouled over the years and when that happens, stalling, high or low idle problems etc. pop up. You can remove the valve and try cleaning it, sometimes that is enough to get it back to spec. It is a large screw in pintle type valve located in the throttle body right near the throttle blades.

[Injuneer]

Don't use the generic table in Haynes, etc. Go only to the LT1-specific code list on Shoebox's website. That would have clarified the DTC 28, because it lists separate codes for 93 and 94-95, and DTC 28 is different on a 93.

http://shbox.com/1/Dtcs.htm

DTC 15 = Engine Coolant Temperature (ECT) Sensor Circuit (signal voltage high, low temperature indicated)

This could easilly make it stall and smell rich. When the PCM sees low coolant temp, it assumes the engine is cold, and puts it in a rich condition for cold start. If the sensor remains showing a low temp, even though the engine is warming up, it will continue to run rich, rough, and possibly stall. Run it this way long enough, and you can dilute the oil and damage the rings by washing the lubrication off the cylinder walls. It also keeps the ECM from going into closed loop, which prevents it from correcting the excessively rich condition. Replace the coolant temp sensor. Its the one on the water pump housing.

DTC 28 = Quad-Driver Module (QDM) #3 circuit
applies to:
- fan control relays
- a/c relay

Only the 93 has the QDM and this description. You've got a problem with one of the fan control relays, or the A/C relay, or a faulty quad driver module in the ECM.