my car car used to run and idle fine but i pulled out the motor to relace some gaskets and paint the engine bay. Now my car has a hard time trying to idle and when i try 2 shut it off it stays on even w/ the key removed. i unpluged the coil 2 shut it off and it stayed on another 5-10sec running rough then backfired b4 shutting off... wat could b the problem?