It's very unusual to have to replace a TPS twice in a matter of a couple years. Those parts last a pretty long time.
The A/C compressor puts a load on your engine when turned on, and your computer compensates for that by changing ignition timing, fuel delivery, and in some cases the shifting points of your transmission. (Higher or lower r.P.M.S)
With the age of your vehicle, and the problems you describe, it is very likely that your computer is failing. When computers begin to go, the frequently cause unexplainable problems. Only an experienced tech with good diagnostic skills will have the know how to eliminate other possible causes.
Finally, even if you trust the mechanics who advised you replace your computer, take it to another shop for a second opinion.
Not that your regular mechanic is dishonest, but you'd be surprised at the different levels of experience amongst mechanics and the different advise you'll receive. And you'd definitely want to make sure your computer is actually faulty before you replace it, right?
I hope this helps.
Friday, January 15th, 2010 AT 10:13 PM