Another avenue of checking is the rubber breather hoses the connect to the idle control valve, and the 2 hoses from the smog pump to the engine. I thought the breather hoses were made of a bakelite type material until I replaced them and the new ones were pliable rubber. The hoses from the smog pump to the engine were just old and would pop off on occaision, causing vacuum leaks that resulted in bad stutter at start-up and rough running at low rev. Good luck.
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)