I don't remember if I've posted this before, so excuse me if I have.
When I first got my SLK320, I kept getting a check engine light and the car would go into limp-mode, usually if I hit any kind of bump on the road.
The connection between the air box and the throttle body was dry-rotted, and bumps in the road would open a gap allowing un-metered air in.
To fix this, I cleaned one surface and made a thick seal with sensor-safe silicone, then greased the surface it mates to and gently put the air box back on. After a day or so to finish out-gassing, presto: New air boot and no more check-engine and limp mode.
The air box can be removed and put back on entirely without tools--possibly part of why the boot is a vulnerable to failure--but it does make this fix easy to implement.
Last edited by Jaron; 06-21-2018 at 12:14 AM.
Quick Reply: Frequent check-engine light and limp-mode, especially on bump roads - solution.