The car is a 2005 c230 Sedan (4 cyl) with k&n filter installed at 12,000 miles, car has 19,000 miles now. here goes:

Last week I filled up the car, drove 38 milers to work and as I parked the car, it started to idle roughly and Check engine light (CEL) came on. I shut off the car, started it and same thing. 4 Hours later, I started the car, Idle is fine but CEL still ON. Called the dealer, they said check the gas cap, removed and retightened gas cap, Car is fine, no CEL.

6 Days later, same thing, I haven't filled up since the last time it happened, so I don't think it's the gas cap issue. Yesterday, it started to idle roughly again but the CEL did not come on. The car is fine for now, does anyone have any idea what's the issue here. I'm thinking of replacing the fuel filter as it may just be clogged. Any suggestions?

Not at 19,000 miles..why are you worried about it, the car is still under warranty, take it in, get it fixed..

i will bring it on for warranty work, thank you sir.

i'm just trippin b/c of the horrible stories i heard about these cars, and I really like the car, but if this little annoying things come up, I'm gonna have to let her go. I just hope it's a one time fix. thanks again

Maybe your air filter contaminated the MAF? Just because the air filter is relatively new doesn't mean it was oiled correctly. I believe the wet/oiled air filters are a major source of MAF failures.....do some searching and you'll see.

I would highly doubt a K&N with 7,000 miles on it would have caused a MAF malfunction - but I could be wrong.If you take in for service and they tell you its the cause,tell them to save the speech and replace the MAF.

Who knows Here's my theory after reading about MAF failures and the function of the unit: 'Wet' air filters rely on oil droplets to fine clean air as it passes over them. These droplets are continually under induction pressure to pull them from the foam and eventually enough minute droplets collect to form a big enough drop that finds it's way to the sensor. That's why some people have had good results cleaning the MAF. Some have reported seeing contamination/discoloration on the MAF wires prior to cleaning. More importantly....think of it this way....isn't the air cleaner supposed to stop contaminates from entering the combustion chamber?? How else could a MAF get contaminated unless the air filter wasn't doing it's job or even caused it?

How about the airbox not being seated properly- after filter replacement - allowing contaminates to bypass the filter and enter the engine directly.

I suppose if you were driving behind a poorly running diesel or a gasoline engine with worn out rings there could be oil in the air....but a big enough drop to snake it's way into the engine compartment and into the 'new' intake opening is highly improbable. Besides, there are far to many bad MAF and oiled filter combination failures for this to be the case. Dirt and dust bombarding the sensor wires would render the MAF useless eventually but not give you intermittent problems. Just my .02....oiled filters are dangerous to MAF life.

well I took it in to the dealer, they're replacing a cylinder head now. go figure...

That doesn't surprise me at all, there is a DTB out on the exhaust valves in the 271 engine.

pleae excuse my ignorance but what is DTB, is it some kind of recall?

It is a Technical Bulletin... fixes that come out after the car has been on the road- every manufacturer has them. Recalls are generally safety related, or something that WILL fail for sure. DTBs are issues that not every car will have- like your cylinder head, it's due to carbon buildup on the exhaust valves, so the car misfires under certain conditions- it won't happen to everyone, based on how you drive the car, type of fuel you use,etc..

thank you so much for sharing your knowledge power.

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