'98 C280 Rough Idle
 

My c280 is experiencing a real rough idle. It started out only running rough at idle in drive, but now it runs rough at idle in neutral too. I have replaced the MAS but it didn't help. The car runs great any other time. Anyone else had this issue?

I'd change the spark plugs and the coil supressor boots.

Use only the OEM Bosch non-resistor type spark plug.

98% of all rough idle problems on M104 engines are caused by these coil supressor boots.

It's a 98, so it's a M112, not 104.
Is the check engine light on?

Gilly

Had a check engine light but it went out after changing the MAS

How many miles is this unit sportin', and what kind of maintenance has been done on it? Spark plugs, air filter, fuel filter, any of that been done lately? Are you running premium in it?
Gilly

PS Did you replace the MAF sensor yourself, and if a shop did it, did they say anything about "resetting" the "adaptation"?

Did the MAS myself, Filter have been changed and I am going to do the plugs this weekend.

Oh yeah 83,000 miles

Try the plugs. The engine control module could have also lost it's ring gear self-adaptation, it would need to be checked using the shop computer SDS.

Gilly