What would make the car idle too high on start up but slow down as soon as you started driving it? I recently did a bunch of work to the car replacing the fuel injectors, crank position, throttle position, coolant temperature and oxygen sensors and the thermostat. I also replaced the intake manifold, plenum, throttle body, EGR and valve cover gaskets. Changed the spark plugs and wires. The car has been running great and now all of a sudden it idles too high on start up with a cold or warm engine. Today I let it run for a minute and the check engine light came on. I turned the car off and checked under the hood to make sure all the wires and connections were tight and they were. When I turned the car back on there was no light and it never came on again. Any ideas?