If the idle timing is off by even a few degrees, it can cause your engine to run at less than optimum efficiency. The farther off the timing is, the worse the engine will run until it won’t run anymore. Checking the timing can be done in two ways. The first and easiest way for inexperienced mechanics is with a timing light. The timing light is connected to the battery for power, and has a wire that clips to the spark plug wire for the number one cylinder. A light that flashes when the spark plug wires are pointed at the crankshaft pulley near the block, and a mark on the crankshaft is compared against a scale on the block. More experienced mechanics can feel and hear the engine running less than optimally.