95 e300d rough old idle (still!)
 

I have been trying to fix this rough idle for a while now. The car starts fine when cold, just idles badly, acts like a gas car with a misfire and some bluey smoke (but not too much). As soon as it warms up it is OK. The glow plugs have been changed and all the fuel lines have been changed, along with the "run off pipes" that run along the length of the head. I have changed the seal in the pre filter and main filter again. I have not changed the shut off valve.

An air bubble appears in the top of the clear line from the pre filter to the fuel heater when the car is left for a couple of hours - the bubble is about an inch long.

Would it prove anything if I were to set the shut off valve to "off" - and then see if the air bubble still appears?

Thanks for any help

The bubble (actually, fuel draining back) in the line you mentioned is normal.

Have you tried a diesel purge? Could be you have an injector with a bad spray pattern which gets better as the engine warms up.

I have heard of a diesel purge but not sure what it is or how to do it?

Take a look at this post. It should explain how to hook your lines up.

http://www.peachparts.com/shopforum/diesel-discussion/113596-e300td-diesel-purge-proceedure-solved.html

Diesel Purge is made by Liqui Moly. In the US it is distrubuted my Lubro Moly.

Be certain to turn engine off before runing your temp tank dry or you will have a lot of air to purge. Most find two cans better than one.

I have the same car, and same problem, but no blue smoke. diesel purge is a good thing, it does something and the setup is easy. look it up at diesel giants website.

If it was fuel/injector related then it would typically NOT get any better when the engine warms up. However other likely possibilities are:

1- Defective over-voltage protection relay.
2- Defective engine/computer temperature sensor
3- Defective Wiring ( Very Common on this model)

Been there, done that

Phil

How long does it take for the idle to smooth out?

How many miles?

I had a rough injector get better as the engine warmed up. Cleaning fixed that. I didn't detect anything amiss in my 99 E300 at 100K. Took injectors out for cleaning and checking. Turns out one has bad spray pattern and low pop off pressure. They cleaned it out and the car has been running smoother than before or so the wife says.