Hello
Weather getting cooler again and now my 2005 C240 is sounding rough untill warm. Like a truck!
Any ideas? It happened 2 years ago and I brought it to the dealer. they charged me $240 to change the engine mounts under warranty and "retorque" the transmission/exhaust bolts. Made no sense.
I think it is a sensor or other item that operates until warm...Or is not operating properly.

thanks

first 30 seconds when starting a car idles higher than normal to heat up the cat converter whether its cold or not

Clean the MAF. What mileage has the car done? Are O2 sensors in good condition? You might not be getting proper mixture enrichment when cold.

Does the car stumble when you pull away cold?

hey glen im hearing a hissy noise when im in the rear of the car by muffler

any ideas?

I think that's a normal thing for a I4 engine. I have an 05 c230 with 38k miles recently serviced B from mercedes. Mine when started sounds pretty loud and very unlike a luxury car. I think that's the drawback of an inline engine. When it warms up it sounds much better.

The four-cylinders are certainly loud and unflattering, especially given how great the car looks at the same time how not great it sounds.

But I don't hear any hissing noises by my exhaust. Some burbling but no hissing.

Experiencing the same thing...I always assumed it was normal with the cats needing to warm up and all.

Glyn - Can you tell us what it means when the car stumbles when pulling away cold? Happens to me all the time. Is it time to clean the MAF?

Not trying to thread jack, by the way.

Possibly clogged Cat or a piece of Cat honeycomb has broken off & is clogging something. Presume no area of the exhaust has been damaged on a speed bump or similar? Might have a hole in a pipe or muffler/silencer.

Engine stumble = flat spot when you pull away instead of pulling cleanly. Modern fuel injected cars in good tune should pull cleanly from a cold start if the mixture control is perfect for any temperature. The joys of fuel injection over carburettors.

It's time to look at the MAF & upstream O2 sensors. Check if the car is storing any codes.

hahaha i told this to the dealership...they "ran" a leakdown test and found no leaks...

OK I will check those out. But it works fine in summer, even on cold start. Drive 5-10 miles to warm up and its ok. Does not seem to stumble. but to be honest it sounds so bad I pamper it till its warm!

thanks

Just checked with my OBDII tool and no codes show up. I am at a loss? should I just go and clean the MAF sensor?
I would have expected bad O2 sensors to throw a code. However my understanding is that the engine runs open loop until the O2 sensors are warm anyway so there should be no change in condition while engine is cold if the O2 sensors are bad.

thanks