Why do idle RPMs go up and down?
Why do idle RPMs go up and down? The higher idle allows the engine to run while the air fuel mixture and timing are less than optimal. On the car with the idle that was going up and down, the ECU was likely trying to calibrate the inputs and output to get the idle where it needs to be. Why does my engine tap when I start up? Upon start up, the lifter will take a few moments to “pump up” and expand as the oil pressure builds in the engine. During this time, the valves may tap since there...