I have a 1990 240DL. The car starts just fine, but when it warms up the idle is erratic. It will idle very fast and this will last a few seconds and then it will return to normal idle. It repeats this while sitting at a light it runs fine when the can is in gear and under power. Please can any one help?

 

perhaps your idle air controller is sticking open intermittently? they get pretty gummed up with age. this is located under the intake manifold, and has two mid-sized rubber hoses that connect to either side of the throttle body.

 

Thanks. I'll check that and see if it fixes the problem.