Car is a 95 W124 E300D with 155k miles.
I have just replaced all 6 glow plugs to fix a starting problem. That is now fixed but the idle when cold (only very cold - icy mornings) is uneven - the revs hunt between 550 and 700 rpm. it is not very serious does not stall but it is annoying. Once warmed up it is fine. Starting from hot and cold is also good - as soon as the key is turned.

There are a number of other observations but dont know if they are linked.

When starting from stone cold there is a very slight hesitation in the turning over of the engine - bit like a slightly discharged battery - but the battery is 6 months old Bosch unit.
There is air in the diesel supply pipe leading to the fuel filter.

Any ideas?

Thanks

Has the engine wiring harness been replaced?

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Jim

No wiring harness is original; I did not think that this problem afflicted this diesel engine?

I don't know. I was just curious. I am changing glow plugs on an E300 that I rolled into the shop a week or so ago. The complaint was "bad idle". Never got much more description than that. I did find two glow plugs bad and the wiring harness is awful. In the places where the harness came closest to the block and the single wires were exposed the insulation is totally gone. Everywhere else it is cracked all to heck and back.

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Jim

Thanks I will check it. I doubt this is the problem. Out of interest what year is the car you have?

It is a '95 too. I am waiting for the delivery of the new engine harness and will report in after I finish changing it out. Based on talking with the lady owner the car has had nothing done to it other than oil/filter changes and brake pads since she purchased it new in '95 and she has asked me to go through and replace everything that is worn out or needs to be replaced - kinda playing catch up on maintenance. Anyway, the in-cabin filter was in AWFUL condition.

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Jim

If the plastic fuel lines have not been replaced, it's time. Air in the lines is not a good sign. Causes hard starting and hesitation, rough idle.

Rgds,
Chris W.
'95 E300D

Thanks guys. I have already replaced one of the plastic fuel lines - a short stubby one on top - I think that was leaking slightly last year. I have two more on order - the ones that have air in them.

Will let you know

Just add - the strange thing is that starting is great hot and cold.