My c230k has a erratic idle when coming to a stop.
It goes to almost zero and after a few sec goes back up to nrm. Sometimes the engine dies altogether.
Pain in the *** when at junctions.
The c230k engine is basically indestructible, it's highly reinforced compared to the NA 4 cylinder engines and apart from cracking the odd exhaust manifold it should be very reliable! I have heard of the mass airflow sensor causing problems like the one you describe, it could also be bad fuel or the ecu going insane.