Mitsubishi Repair: Power/gas mileage problems, mitsubishi 3000gt, intake air temperature sensor

Question
I have a 1994 Mitsubishi 3000GT base (DOHC, auto)  My car has a few problems that have come on kinda suddenly.  I have a hard time starting in the cold,  the idle fluctuates up and down when cold(1400-1900rpm).  If i start driving before any temp shows the car stutters and lurches?  When it warms up all that stops except for a slight idling fluctuation (600-800rpm) up and down every few secs.  When it is warm now it is gutless up until about 3800rpm and even then it still doesnt have the power it should.  It also seems to not want to downshift as quickly as it should.  This is a more than regulary maintained car, oil, filter 2000miles, air filter every 5000miles.  spark plugs every 8000miles,  trans oil+filter every 20,000. My mileage is down to about 10-11 MPG. ANY IDEAS????

Answer
Carl: Got an AutoZone close by? For free they will code your car, that would rule out any problems with the computer or sensors. I think you have a weak sensor someplace, the fact that it starts hard makes me think of that. I would be looking at the intake air temperature sensor(IAT) but also look at that computer. You know don't you that Mitsubishi farmed the building of their computers out to another company, which did not do a good job with them. A piece will start to leak into the computer and with time kills off the computer. Sometimes the computer having problems will show up like what is happening to your car. So have the car coded would either explain your problems or rule out the computer or sensors as the problems. I would look that way as long as you have taken such good care of your car. I hope this helps and good luck! Linda