2004 Chevy Impala 3.4L base, accelerates on it own

Hi all,

I recently purchased a 2004 Chevy Impala 3.4L base with 68k miles on it and I am having a problem with the acceleration and coolant level.

About every other time I start the vehicle, the car accelerates on its own, to the point where I am riding the brake when driving on a level road. When the car is engaged in park, it seems to be idling high. Also, when the car does accelerate on its own, I can hear a high-pitched whistling coming from the engine.

The coolant level has been under the cold mark for the last few days. I have added approx. 1.5-2 quarts of Dex-cool. Today it stayed at the cold line and did not require more fluid. I was alerted to the problem because I could hear liquid flowing sounds coming from the dash.

Any advice on what I should do? I have brought it back to the dealer and he has been willing to work with me, but he was not able to replicate the acceleration problem.
The dealer did tell me that the lower intake gasket had been replaced recently. I took apart the air intake and cleaned the throttle body and the IAC, but it hasn’t helped.

Thanks for any advice.