Pontiac Repair: I have a 92 Pontiac Grandam..., mass air flow sensor, throttle position sensor

Question
I have a 92 Pontiac Grandam se 3.3l v6 engine. The engine had been replaced before I bought it and I believe it had a smaller engine one of the 2l engines in it. The car has reved up and down in park ever since I got it but now it does it while I drive and it has quit on me. I have had it to several mechanics and bought several parts and it still does this and I think it's getting worse. These are some of the parts that have been replaced-fuelpump+filter,waterpump,mass air flow sensor,and just recently some kind of idle part an arm or sensor control mabye. I've replaced so many i've begun to lose track. I also had the system flushed and the oil+filter replaced recently. I'm sorry this is so long but I'm desperate and can't seem to find any help or get a straight answer. I forgot about the plugs and wires I just recently changed them myself. I beg of you if you have any ideas please let me know. I
can't thank you enough for your help.

                         Jackie Lambert

Answer
Hi. this sound like the throttl position sensor. if you have not changed it. have it checked, check for a intake air leak. A air leak at the throttle body will make the idle go up and down.The throttle position sensor will cause the engine to idle up and down.