High Idle - Causing major headache!

Hi there....I am hoping to get some help here. I bought a used 2001 Olds Intrigue GX in June of 2003. It has a 3.5 V6 engine and it is an automatic. It has around 54,000 miles on it (bought it with 46,000). About a month after I bought it I started the car and it ran up to 3500 rpm....I shut the car off and turned it back on and it did the same thing...I can do that about 3 times and then it will be fine. It happens quite a bit when I start it and does also happen while I am driving...the car just wants to go and if I stop or put the car in neutral or in park it flys up to 3000-3500 rpm instantly - when I drive, it goes down to about 2000 - 2500. It makes it difficult to stop too. I have taken it to the dealer and to a private mechanic 2. I had the Idle air control valve cleaned once, that didn't help...put in a new Idle air control valve, that didn't work. Nothing shows up on the computer - as in any codes either. It doesn't matter if the car is hot or cold. It happens intermittently. My mechanic thinks it could be the computer, but he doesn't want to replace that if it isn't the problem....Any suggestion would be great.

Also, the car uses about a 1/2 to 3/4 of a quart of oil between oil changes (2500). Most driving is done on interstate. I use 5w-30.

Always wanted an Intrigue-owned a cutlass supreme 3.1 v6 and it was great. 180,000 when I sold it....this intrigue gives me the creeps!

There is another thread on this board with someone else who has a similar problem. I don't think that the IAC valve can pass enough air by itself to sustain a 3.5 L engine at 3000 RPMs. I would look for a stuck TB or something strange with the cruise control.

thanks for replying, I will try anything