Rough idle when cold...smooth when warm..?
Just performed the 100k mile service, new plugs/wires,air filter, oil, trans flush etc.
On cold starts I get some vibration and what feels/sounds like misfires from the motor. The car surges and hesitates occasionally on acceleration, deceleration and in between shifts. The vibration continues in Park or Drive, at stoplights, etc. for 15-20 minutes. After the car is warm, the idle is perfect and the car drives great. No CELs.
My indy mechanic believes the problem can be fixed with a new fuel filter/pump (the one on the top of the tank, not the one in between the fuel banks that would require a whole new tank).
Question for you guys with the 55k motors is, have you experienced this type of an issue? Was the problem a faulty/clogged fuel filter/pump? Was it something else like an EGRV? An idle control valve?
Any input would be appreciated. Thanks
-Ken
Last edited by Ken311; Dec 9, 2013 at 09:37 PM.
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It's required service around 60K miles.... expensive, yes but important. A lot of guys seem to miss this service item either because they think it's too expensive (~$600) or they just never realized it was supposed to get swapped out.
Clogged filter = low fuel pressure & flow. At WOT, you could end up starving the motor for fuel... and that's when the REALLY expensive problems happen.
I don't know if there is a way to read fuel pressure through the OBDII port or not, that would a convenient way to do a quick "sanity check" on the condition of your fuel filter/pump....

-G
The Best of Mercedes & AMG
It's required service around 60K miles.... expensive, yes but important. A lot of guys seem to miss this service item either because they think it's too expensive (~$600) or they just never realized it was supposed to get swapped out.
Clogged filter = low fuel pressure & flow. At WOT, you could end up starving the motor for fuel... and that's when the REALLY expensive problems happen.
I don't know if there is a way to read fuel pressure through the OBDII port or not, that would a convenient way to do a quick "sanity check" on the condition of your fuel filter/pump....

-G
Thanks,
Ken
Just performed the 100k mile service, new plugs/wires,air filter, oil, trans flush etc.
On cold starts I get some vibration and what feels/sounds like misfires from the motor. The car surges and hesitates occasionally on acceleration, deceleration and in between shifts. The vibration continues in Park or Drive, at stoplights, etc. for 15-20 minutes. After the car is warm, the idle is perfect and the car drives great. No CELs.
My indy mechanic believes the problem can be fixed with a new fuel filter/pump (the one on the top of the tank, not the one in between the fuel banks that would require a whole new tank).
Question for you guys with the 55k motors is, have you experienced this type of an issue? Was the problem a faulty/clogged fuel filter/pump? Was it something else like an EGRV? An idle control valve?
Any input would be appreciated. Thanks
-Ken

I'm going to have to start checking more possible problem areas. Taking a look at the throttle body/actuator plate this week as well as the secondary air pump. Could it be a vaccum leak?
I have written off any issues with plug wires because it would be causing rough idle/operation all the time...same with O2 sensors (had these go bad on my C32 and they throw CELs). It's very confusing that the car can run so smooth when warm but so rough when warming up.
Last edited by Ken311; Feb 4, 2014 at 04:32 PM.
However, on cold starts the idle is still very rough. After 5 minutes, it goes away and the car is smooth as silk. This is making me lean to the secondary air system, but I am just beyond confused as to why a malfunction in this system would not be throwing a CEL or at least some error codes while the rough idle is occurring...
Input...suggestions?

i was referring to the "sneaky ecu reset" with cycling the key. it surely can't replace a hard ecu reset, but i'll see if it helps at all
Good luck
Good luck
Good luck




Since then, I have noticed there are some remaining vibrations (severity is much less) during startup and certain scenarios when driving. With how well the car is driving and idling now, I believe my problem may be worn motor and/or transmission mounts as they have not been replaced during the car's 97k miles. I'll be taking her into the shop in a week or two.
Hopefully my experience can be helpful to others who experience poor drivability with their AMG's!
-Ken




