First off before I did any work this was not happening. I put a new thermostat in and changed a coolant hose. When everything was put back togehter and I started it the motor will rev real high then low then real high then low constantly. Only thing I can think of is the hose that mounts into the sleeve between the throtle body and the air cleaner came completely off. I had a real hard time trying to figure where the end behind the motor was supposed to go. It was dark and there is very little room. Would this not being connected or connected in the wrong spot be causing the problem? It was a tight fit. I may have knocked some other vacuum line off or something while trying to get to it even though I was being careful. I've never seen a vehicle react like this. There is probably a 3-4000 rmp difference when it is reving up and down.

One other question I have is there is one more coolant hose I need to replace. It is on top of the motor and behind it. It doesn't have the typical hose clamp. It looks like the clamp is built into the inside of the hose and it is plastic. Any idea how to disconnect this thing?

Thanks in advance!

What engine and year? From the sounds of it I would start looking over all the vacuum lines.

Sorry I didn't mention it is a 2001 Olds Silouette. I think it is the 3.8L

Also look over the plugs on the throttle body, Idle air control, and throttle position sensor.

According to Wikipedia, the second-generation Silhouettes only came with the 3.4*L engine.

Can you post a picture of that part of the engine bay?

Thanks for the replys. I wasn't sure of the motor. Just got the van on a budget beater special. It is a 3.4L motor.

The problem was human error when I was putting things back together after replacing the thermostat. I had the bracket for the throtle cables on wrong and it was locking the throtle open. I assume it was hitting the rev limiter. It was an easy fix and it runs great now.

Thanks

Good to hear.