Mitsubishi Repair: Mitsubishi Diamonte LS 1999, coolant temperature sensor, mitsubishi diamonte

Question
My car has been idling VERY rough and at times it almost shuts off when I come to a stop in gear or if it idles in park.  I had my shop mechanic at work change out the plugs, wires, fuel filter and they cleaned the injectors - but it still idles the same.  Could it be the EGR valve?  The engine did not put out any codes on our computer.
Also, just in the last week on 2 seperate occasions - I have been driving and the temperature gauge will start going crazy for just a few seconds and then it goes back to its normal spot.
What is going on with this car?

Answer
Teresa,
A clogged EGR valve can cause a rough idle.  Other items like a bad PCV valve, leaky intake manifold gasket, faulty idle air controller, or a stretched timing belt can cause poor idling.  If the timing belt is old and has not been replaced in over 60,000 miles, it should be changed and the timing be set properly.  Another item that can cause the problem, and may be related to your thermostat problem could be your engine coolant temperature sensor.  If that sensor is faulty, it'll send the wrong information to the car's computer that can adversely affect the IAC and ignition timing that could cause poor idling.  Have your mechanic check those items if he hasn't already.
Good luck!