VERY Rough Idle after 2500 mile drive... - PeachParts Mercedes-Benz Forum

300SD81 · #1 05-11-2009, 07:09 PM

I need some help here. I have some extremely rough idling that smooths out as soon as the engine rises above about 2000rpm. It shakes violently ans lets out puffs of smoke under 1500. It happened after cruising at speed half way up here to Edmonton, Alberta, and the car runs fine as long as I don't let it idle. No idea what caused it, and I need the car for work ASAP. It also won't start very easily and can stop sometimes when the idle gets too rough.

JEBalles · #2 05-11-2009, 07:17 PM

What color smoke? Valve adjustment, peut-etre?

SD Blue · #3 05-11-2009, 08:47 PM

This sounds like pretty typical symptoms for a worn/misadjusted rack dampner screw.

TMAllison · #4 05-11-2009, 09:44 PM

Any fuel leaks on the supply side letting air in the system? Takes a pretty good leak to kill one once running.

Diesel911 · #5 05-11-2009, 10:40 PM

I vote for an Air Leak or maybe you got some bad Fuel.
For either you can fill another container with good Diesel Fuel and disconnect the Fuel inlet hose and replace it with a hose long enough to run into the Container.
See if it runs OK that way.

awsrock · #6 05-11-2009, 10:49 PM

Injector hard lines broke, perhaps? I had a crack develop out of nowhere at the nut on the IP side of one of my lines, and it was making one cylinder work at "half power"..very rough idle. However, the fuel was coming out of the nut, which is how I know the line was the cause. Just something to consider...

dieseldan44 · #7 05-11-2009, 10:53 PM

Check your injectors, listen to them with a stephoscope to see if you can hear anything strange. the smoke probably is unburnt fuel perhaps coming from a poor spray pattern or a poorly timed injection (bad injector spring).

When idling, unscrew the injector line at the injector and see if when one injector is 'turned off', there is no idle change - meaning the injector isnt firing at idle.

Doing a diesel purge would also be helpful to rule out bad fuel.

300SD81 · #8 05-12-2009, 12:53 PM

Its also extremely difficult to start now that the engine isn't hot anymore. I pulled the rack damper and it seems to be fine. Will be doing a valve adjustment and having a look at the fuel later today.

Diesel911 · #9 05-12-2009, 02:27 PM

When I was a Kid an Old Timer told me that when you want to find out what is wrong' fix only 1 thing at a time. If you fix several things at a time you will not know which one caused the problem.

bgkast · #10 05-13-2009, 12:05 AM

Sounds like it could have one cylinder missing at idle. When it is idling try cracking each injector line and see if one does not change the idle sound. If you find one that does not change how the engine is idling you have found the cylinder that is missing.

300SD81 · #11 05-13-2009, 01:04 AM

I can't even get it to idle at all anymore. It takes a lot of effort to start, on jumper cables.. Didn't get to do anything today because it SNOWED... Hopefully going to adjust the valves and inspect the injectors tomorrow.

Bob Albrecht · #12 05-13-2009, 11:14 AM

It could be a combination of a clogged secondary fuel filter and weak/unbalanced injectors. Try the fuel filters first if you have not done that already.

holtonmusicman · #13 05-13-2009, 04:23 PM

I am having similar problems...however mine starts quite easily first time.

Could injector (IP) timing be off? Start of delivery? I know mine is not bad fuel as I've run her nearly dry then half a tank of quality fuel then full tank at my local truck stop plus injector cleaner.

It's weird.

Occasionally she will idle smooth, but typically, below 1500 she idles poorly.

VERY recent development as well...ran great one day, idled poorly the next.

JEBalles · #14 05-13-2009, 04:30 PM

Snowed? Where is it still snowing in May? You in the Rockies or something?

300SD81 · #15 05-14-2009, 02:41 AM

Adjusted the valves today, SHE STARTS! and idles fairly well. What are the chances that I have burnt valves now? The intake valves were EXTREMELY tight, not even closing, no idea how that happened, since I had just adjusted them less than 15k miles ago... Still seems to be some injector nailing, but I'm working on getting a new set of injectors sent up here...

Its snowing here since I'm up in Canada for the summer working as a tech for APX Alarm.