94 sc2 intermittent rough or fast idle

I have a 94 sc2 with 177,000 miles on it occasionally it will not idle and run with a slight miss, after it does this and you shut it down a few times then it starts to idle fast. I read that a plugged fuel filter might cause this and changed it but the problem returned. The service engine light is on, can you jump the pins with a paperclip and get the codes on this particular vehicle? Is there a sensor or something that might be causing this? Hopefully someone can point me in the right direction.

paperclip trick - http://www.differentracing.com/tech_articles/diag_info.html

how old are the plugs wires?

this is probilly a bad ECT, i don't have time to go into detail now, but search the forum and you will find everthing you need. otherwise, post the codes and we will go from there.

The coolant temp sensor can cause this and they are known problems.
Replace with an oem all brass tip. If no service has been done recently check the air filter, plugs, wires, vacuum hoses, pcv valve, And it wouldn't hurt to clean the throttle body,AIC valve, and Egr valve.
:2cents:

plug wires are 3 or more years old, plugs maybe 2 yrs. ECT sounds like a good diagnosis, does the ect have any bearing on the fan coming on and off? My fan quit coming on so I had put a jumper with a switch in place of the relay, the relay seemed ok so maybe its the sensor affecting this as well? pcv was changed recently, what is the AIC? Where is the egr located?

I'd go ahead and change your plugs out, also gives you an indication of other problems and engine condition by the condition of the plugs

peppermrj meant the IAC, Idle Air Control Valve, it is located inside the throttle body... Both the IAC and the TB are easier to clean with the TB removed (be careful with that gasket)

Your problem may be as simple as the ECTS, which has messed up SOO many peoples cars, causing similar problems with the A/F ratio...
might want to check the ECT sensor and the IAT sensor to see if they are giving you a proper resistance for the outside temperture...

The ECTS is located on the block under the radiator hose Black and Yellow wires lead to it

BTW the ECTS is ~$10 from SaturnParts.com + S/H

The IAT is located in the air intake duct, right before the filter box

You can check the condition of the ECTS or IAT by taking the wiring harness off of it and using a multimeter set to OHMs and probe it to see if you get the proper resistances... (see below)
or simulate conditions by taking out the ECTS and placing it in cold water then slowly heating the water to make sure it gives proper resistance throughout the temperture range, or a hairdryer for the IAT

while you have the connectors off probe the harness side with a multimeter set to 20DCV and see if you are getting ~5DCV as a referece voltage with the ignition in the on (not started) position


Here are the resistances for the ECTS or IAT in various tempertures
-20 degrees F________39K-53K OHMs
0 degrees F__________21K-27K OHMs
60 degrees F_________3.9K-4.5K OHMs
120 degrees F________1.0K-1.1K OHMs
160 degrees F________430-480 OHMs
200 degrees F________215-235 OHMs

My fan quit coming on so I had put a jumper with a switch in place of the relay, the relay seemed ok so maybe its the sensor affecting this as well?


BINGO! thats more then i needed to hear. change the ECT.