Service soon light on,cuts off when at idle,hard to start back.

The information below was complied by me, it explains what causes the check engine light or Service Engine Soon light to come on and the process of finding the cause.

When the Check Engine light or Service Engine Soon light (depends on make) is turned on the computer control unit (called the PCM) has sensed a fault in the electronic controls of the engine and/or the emission system. When this happens you will seldom feel the car engine run any different. There are about 200 possible faults that turn the Check Engine light on, to know what has developed a problem you must have the system tested, this is called an OBD2 fault code test, Kragen and Autozone parts stores do this testing for free.