My 300CE puffs out some smoke from the engine breather hose. Also some oil deposits inside the air filter cover. Is this normal for a M103 motor? I get an occasional misfire and one wet-oily (engine oil) spark plug is usually the cause of the problem.

One MB service technicians say it needs new piston rings. The other says a valve job would suffice. A Compression Test was performed and within Mercedes specifications.

I have changed the following in the past 6 months:

Ignition Sender Unit
Ignition Coil
Ignition Distributor
Ignition Distributor Cap
Vibration Absorber / Balancer
V-Belt
Fuel Pump Accumulator
Fuel Pumps x 2
Fuel Filter
Fuel Injector Nozzle / Seals
Fuel System Valve

I have not replaced the Ignition Cables. Could this be possibly the cause?

Otherwise, the car runs very smoothly, no oil/smoke from the exhaust. What gives?

I have an M103 in my 300se with a similar puff of smoke from the breather hose. Not saying it's suppposed to happen but with engines as worn as these it is inevitable. I assume that's why the vent hose was installed. If your compression checks ok then it's likely not a big problem.

I also have a similar rough idle problem. I think eveyone deals with it. I've checked all of the electrical components in the CIS-E system and all seem to test out fine. At one point I pulled the connector off the cold start injector thinking it was the culpret. No change. Yesterday I actually removed the fuel line to it and capped it at the fuel dristributer. Big change. Still slight roughness but a significant improvement. Sitting at a stop light you almost can't tell it's running. My assumption is that the cold start injector is leaking under pressure. I'll replace it before the cold weather sets in.

Sounds like your engine needs new valve stem seals.

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Fred Hoelzle