is not running right like before
check engine light on 1991 BMW 525i
it could be a variety of issues...the most likely one could be that it is time to have the spark plugs cahnged and the car is due for a stage I tune up.
When the check engine light comes on a diagnostic code(s) will be stored in the engine control module, and this code(s) will need to be retrieved to know where to start diagnosing this problem. This will need to go to a shop if you are not familiar with diagnosing and repairing fuel injection/ignition issues.