My 98 SC1 (96,000 miles) starts rough when re-starting between 1 and 6 hours after running. It seems to run rich initially, then after about a half minute it runs smoothly. The spark plugs and wires are good. The fuel filter seems to be OK, since the engine doesn't bog down when accelerating. Any suggestions?

Mr. Physics

 

Coolant temperature sensor would be my first guess. Pull it out and see if its a plastic tipped one or brass. Most likely its plastic and faulty.

 

Low Saturn (Mike),

Thanks for the suggestion. I went to an auto parts store and picked up a coolant temperature sensor. They suggested that I check the IDLE AIR CONTROL (IAC) valve to see if it was gummed up. I did that first - unplugged and removed it (after waiting more that the minimum 10 seconds after the car had been running, per repair manual instructions) and cleaned it with carb cleaner. I also plugged the IAC valve connector (wires) into the IAC valve with it out of the throttle body and turned the ignition key to the run position - the pintle moved, so I assumed the IAC valve was OK. I re-installed the IAC valve and started the car. It still started roughly. I then took out the coolant temperature sensor. It had a cracked plastic tip. I replaced the sensor with a brass tipped one and the car started with no problem. However, I now have to have the idle speed screw turned all the way in to keep the engine from stalling (about 950 rpm). I'm wondering if the IAC valve may be bad or out of adjustment since I put power to it when it was out of the throttle body. Any suggestions?

Mr. Physics