Ok my 90 olds cutlass ciera might have an issue with the computer. its a 3300 V6. It would start hard when its cold and idle really rough. I replaced the coolant tem sensor. it didnt work. at the shop we plugged it in and the computer was reading 250 degrees and a thermometer reading of the coolant read 120. We think it might be the computer but we couldnt find where it was. Can anyone enlightne me?

 

Why do you think it is the ECM? Did you get the auto shop to pull your trouble codes? If you had a bad ECM chances are you would have a code for it. Quad driver modules are a part of the ECM that fail on early GM Type I cars. I had to replace the ECM on my 93 Buick LeSabre. It was behind the glove box. If you replace the ECM then you need to have the proper equipment for electro static discharge. This is a mat with a grounding wire and wrist band that prevents you from striking the ECM with lightning when you touch it.

 

well i said in my post that we plugged it in to the scanner at the shop. The new coolant sensor reads over 250 according to the ECM. we took a thermometer and tested the coolant and it was only about 125 degrees. The computer thinks its running really hot all the time which is why it starts really hard. thats after putting in 2 coolant sensors. My mechanic says its got to be something with the ECM.

 

Where did you measure the coolant temp? Make sure you measure it where the coolant temp sensor is. You want to compare apples to apples.

As I said, I doubt it is your ECM. Why would your ECM fail exclusively in the circuit that controls and monitors the coolant temp sensor? Don't forget that an ECM is just a simple computer. If it failed then that means there is a circuit or component on the card that went bad, and that isn't likely to happen.

If your mechanic can't give you anymore advice then you have two options.

1) You can continue to search for an alternate cause.

2) You can have your mechanic replace the ECM and hope for the best.

If you don't have the time or ability to continue to troubleshoot it then I would suggest you tell your mechanic to simply "fix" the car. If he decides to replace the ECM and it doesn't "fix" it then it is on his shoulders. Good luck!