Matt;

You may want to check your throttle plate and make sure it is fully closed when in idle mode. Loosen the lock nut on the throttle plate and back off the adjustment screw until it does not touch the throttle plate. Start the car and see if the idle speed corrects itself. If it does, turn off the car and set the adjustment screw so it touches the throttle plate contact and add about 1-1/2 turns (and carefully lock in place with lock nut). This will help prevent the plate from hitting the throttle body when closed. I had a high idle problem that confused me for a few weeks until I tried this adjustment. Clean the throttle body also (if needed). It is a very small adjustment that may be causing your problem. While you have the accordian type plastic air intake hose off, check to make sure it does not have any holes. It can add unmetered air into the fuel mixture that impacts fuel efficiency and economy. Repalce it if it has any holes. Hope this helps.

Rustydog
1986 240DL
147K