w211 220cdi hunting idle problem

[haydar]

Hi all

My 220cdi W211 when first started in the morning starts hunting on idle. It's very slight. The exhaust seems to give off unburnt fuel (makes your eyes burn slightly). However, as soon as the car warms up a little it no longer does this and the idle is perfect for the rest of the day. Even if the car is left unstarted for the whole day and started in the evening, the idle does not hunt!!!!

The car's injectors were checked to be all OK, the compression on the cylinders was checked and again OK.

One of the mechanics was suggesting that it could be the Catalyst is on the way out? Could this really be causing the problem? Could it be one of the injectors that only causes the problem once it's been left out in the cold over night?

All advice appreciated.

 

[Sprint'n'Go]

I may have experienced similar to this on my van (270CDI) and an earlier 311 (220CDI) but if it is the same thing then I would describe it more as a misfire, i.e lumpy chuggy running until engine has run for approx 10-15 seconds then fine again all day and often for weeks. I reported it to mercedes with the 311 and was told all was fine and a diesel couldn't missfire. it continued to happen occasionaly every few months, usualy after a cold night and a weekend of being parked up. It never became a problem, just an annoyance.

My 316 started to do it when it was about 6 months old and this time mercedes reacted completley differently and changed all 5 injectors under warranty(they said one was faulty but they are changed in sets).

It has happened once or twice since but I reckon it is probably dampness in the wiring loom after a cold night/weekend or more likely, an injector sticking when cold.