90 300e Won't Idle
 

My 1990 300E won't idle and requires depressing the gas pedal slightly to restart. The car has had slow/rough idle when first started lately. Also, one time after it died, I was able to restart the engine and the check engine light flickered with a slight change in the exhaust note each time the check engine light came on. The CE light does not stay on (are codes saved when fault occur?) and how do you retrieve codes? Any help will be greatly appreciated.