99 E300 Diesel rough idle
 

My 99 E300 TD with 218K miles idles very rough, hot or cold. When this first started it would smooth out once warmed up. Now it just does it all the time from start up to a rough shut down. I'm looking for suggestions. Here is what I have done to the car in the past year. Last winter I replaced all the glow plugs and installed new Bozio injector nozzles. I also replaced the fuel filter and pre-filter. Then I replaced all of the fuel lines and o-rings except the ones to and from the tank. I purchased these lines all pre-formed with new fittings attached. Just remembered, Due to a check engine light on my dash, I had the engine scanned and it said I had a bad "air mass sensor". I replaced it with a new one but that did nothing to stop the rough idle. But it did take care of the check engine light. LOL! Any ideas on what my problem may be?

Is it rough only at idle?

It could be an Air leak somewhere. Does you model have a Fuel Heater?

Are you using only Diesel Fuel?

Try running with out the Fuel Fill Cap off.

I have not read of anyone using the Bozio injector nozzles on your year and model until now.
You might hook up your Fuel Lines as if you were going to do a Diesel Purge but run it on Diesel first. If it runs better that could indicate you have an Air leak towards the rear of where you disconnected the Fuel Hose.
If there is no improvement from above since you partially set up for it you might do a Diesel Purge. If that cures it was the Injectors.

There has been a few members who had issues with their Fuel Supply/Lift Pumps. I did not pay attention to the Symptoms when I read there posts.

Some members believe that it is possible for the IP O-rings to go bad and allow Air in but not have an external leak.
Perhaps removing the Delivery Valve Holder clamp (M pumps only) and squirting some thick Oil around the base of the Delivery Valve Holders would temp seal of any Air leak if there is one. This also might work to see if there is Air leaks at any of the other Fuel Line connections on the suction side of he fuel Supply system.

Did you look for air bubbles in the lines? Also, when you attached the new fuel lines, did you "pop" the release clips so that they rattle freely? If not, re-seat all of the connections and release the clips.