High idle/uncontrolled acceleration. Chevy Malibu.
Girlfriend's car has been idling at 3500 RPM when it is in park. When you shift the vehicle into drive, and keep your foot on the brake, the RPM's drop to a reasonable 1500. When you release the brake, the car immediately accelerates to 25mph where the speed will continue to climb without driver input until you apply the brakes. She told me that she has had to replace her TPS twice before for the same problem, so I replaced the sensor and cleaned out what appeared to be a significant amount of corrosion on the interior. Took the car for a test drive, and absolutely no change.
She recently inadvertently drove the car into a flooded section of road and had to have the car towed home. I was able to flush the water out and get the car running again. I don't think it sounded the same when idling and there is a lot of white smoke coming from the exhaust. She swears up and down that it always sounded that way prior. She also stated that she was having issues with the idle/acceleration before she drove the car into a puddle.
My experience is limited, and I will take the vehicle to a shop if needed, but I would rather try to resolve the problem myself if it something simple like changing/cleaning a sensor.