You may want to check the wiring for the coolant temperature sensor. I had an issue with my 1998 Cavalier where this circuit wasn't grounding properly. The pigtail (where the wiring comes out of the sensor) was causing a problem along with aged wires and connections. I had to end up paying a garage to trace the wires and replace them and make sure where the sensor grounds and connects back there is a good connection.
I ended up paying a garage $325.00 to do this work if you can find a COMPETENT garage willing to listen to you and do the work without going through a lot of diagnostics and that you can most likely fix this issue from this for under $100 (even if you get a new sensor which you probably dont' need). I know the garage soaked me with the price but I could not find a garage I trusted to do this. And my father the master mechanic was sure it wasn't the problem. I found about this problem on the internet they did exactly as I thought had to be done but charged me for diagnostics, quite a bit of labor time and other things. It was definitely worth fixing though.
Prior to taking it into a garage I had replaced the sensor with an autozone sensor (figured I got a bad one on a fluke) and bought one from a dealer and was getting the check engine light. Code was like 18 or 22 or somethiing. My father (my normal family mechanic) had me convinced it was the computer (it wasn't of course).
Take my advice troubleshoot the connection from end to end replace the wires/pigtail and make sure you have good connetions. If the temperature gauge in the dash is not working at all or erratically floatiing around particularly going all the way up and all the way back and the car is not overheating this is the problem. This problem resulted in my car having no heat at all sometimes and blazing hot heat at others. The car also tended to idle a bit rough. This sensor is more important than I ever realized.
Sunday, December 3rd, 2006 AT 5:34 PM