RPMS dropping to 200 when stopped

I own a 2001 Pontiac Grand Am with 42,000 miles....recently within the past 2 weeks or so, as the temperature gauge reaches 200, the car starts to idle at 500 rpms. When coming to a complete stop the rpms drop to 200-300. This occurs when in park, neutral, drive, or reverse..as long as the car is fully stopped. The vehicle feels like it is going to stall, but recovers quickly back to 500 rpms. Once I take my foot off the brake, the car is fine...no problems while driving. I took it to Pontiac, no error codes are showing up, and they state that there seems to be 2 slight engine misfires, but they cannot solve the problem until it gets worse and codes show up. There is some history to the car which I dont know if it is relevant. Pontiac had completed a 24,000 mile service a while back and they did not put the engine oil cap back on...oil ended up all over the engine and burning through some stuff. At that time I had engine misfires when the car was shifting into 3rd gear on highway driving. They replaced spark plugs and wires, and cleaned down the engine to solve the problem, but the car has never been the same since! Any ideas??? Please help!!!!

Did you have the engine misfire prior to the 24000 mile checkup? If not I would take the car back to Pontiac, ask for a loaner car and tell them not to call you untill they fixed their goof. If they don"t get back with you in a reasonable time call GM consumer advocate-phone number is in your owners manual. Where they goofed you shouldn't be responsible for any costs.

I have to agree with Lee..dealer would be buying me a new engine...or hear from my lawyer..