Mercedes-Benz Forum banner

Unstable RPM

1K views 4 replies 3 participants last post by  albi.ad8 
#1 ·
hi everyone
Has been some time since my last post. Hope you are having a nice ride with your mercs.
I am having a tiny issue with my w211 220 cdi MY05. For two weeks now when i start the engine and it is cold the RPM are fine and the idle is smooth. When it gets to operating temp. the RPM vary and idle it`s not smooth at all and goes up and down a bit and it`s very irritating. Have read some threads that say it can be the fuel pressure regulator. Is this the issue? What else can make the idle unstable when engine gets at operating temp.?
Any idea is highly appreciated.:smile
 
#4 ·
Reason I rarely chime here nowadays is ridiculous password requirement which I have no chance to remember any more (need to check my pssword avery time)...


But yes it is fuel pressure issue, only culprit can be few different thing...

when it happens some times after start, I would say its fuel quantity valve instead of pressure regulator. Engine starts with regulator controlled and then FQV takes control if I recall right... Many quantity valve faults reported earlier. But then high temperature dependency brings a thought that culprit may be injectors too. I always suggest people to make rather easy injector leak back test when troubles in starting/even run. Test should be done always in same temperature problems occur.

Noodles above is right, SDS would be able perform individual test for regulator, quantity valve and hp-pump, all possible source or faults. Remember there is no fault codes if pressure limits are not triggered. See also injector correction values in ECU. With manual leak test you should be able to find worn injector if any.

Good luck!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top