I took my car to mechanic cause rpm where low. Got throttle body cleaned and calibrated but now on park my rpm are 1600 and the needle jumps higher. Check light engine has turned on. Mechanic put scanner so I assume he put codes in light engine off and car was fine until I turned it back on. Rpm 1600 and engine check light on again. Mechanic says to drive it and it will reset itself. If true, how many miles do I have to drive it? Or what else can it be.