e300 rough idle? air leak? help? - PeachParts Mercedes-Benz Forum

92497pmu · #1 10-02-2006, 11:07 AM

rough idle? air leak? glow plug? injectors? no fuel leaks anymore... help?

1998 e300 TD with 135k miles

Situation:
*On a cool morning, the car starts fine after normal glow
*immediately idles rough (probably 6 on a scale 1-10, definitely not normal)
*less rough when brake pressed and shifted in drive
*not too noticable while accelerating, normal driving... mixed city/ highway
*very rough again when let off accelerator approaching stop
*still rough again while braking, slowing to a stop
*not as bad at complete stop is reached (still in D, drive gear), but car will idle very rough if shifted into Park when stopped or Neutral (stopped or rolling Neutral)
*all symptoms remain the same for at least 15-20 minute commute
*less rough after 1/2 hour or more of driving, e.g a short road trip.
*car runs fine after long drive- no noticable shake, vibration or rough idle when hot or fully warmed up.
*Note, car reaches full 80c temp within 2-3 miles from home (5 min.)
*this rough idle/ vibration has been on/ off for nearly a year to varying extent
*no CEL or GP faults
*no known GP service or replacement to my knowledge (bought car @ 74k- now at 135k but no service book included)

Recently replaced:
*had a major fuel leak, replaced fuel delivery o-rings, copper washers
*also replaced plastic fuel lines at the same time (about 1k miles ago)
*recent fuel filter, air filter, oil change (unrelated, but thought I would mention.
*did NOT replace braided fuel return lines yet.

help please from e300 owners or others with similar problems
- getting more and more frustrated by the day.
Phil

TMAllison · #2 10-02-2006, 01:04 PM

I'm getting vibration from my belt tensioner assembly especially at cold idle. You might check the lower end of the tensioner pivot arm where the damper shock attaches and see if it is causing your vibration.

Could be a weak glow plug at start up with compression creating sufficient heat at operating temp to even idle out?

aklim · #3 10-02-2006, 01:50 PM

How about the Mass Air Meter, fi there is one. I noticed mine smoothed out a little when I cleaned it.

TMAllison · #4 10-02-2006, 02:12 PM

If MAF is malfunctioning should have code PO100 present, right? Its emmisions related.

My expirience with MAF problems is that it is pretty obvious somethings wrong as the turbo is off and the engine wont pull more than about 3k RPM.

aklim · #5 10-02-2006, 02:24 PM

I had a dead spot on my Ford Ranger but no CEL lights. Cleaned it and it went away.

david s poole · #6 10-02-2006, 04:12 PM

with 135k when were the injector nozzles last changed?

veggiebenzE300 · #7 03-29-2009, 01:53 PM

hi, did you ever get the dimensions for the prefilter O-ring? i also need to order a viton ring. thanks!

TMAllison · #8 03-29-2009, 02:09 PM

See post #2. OM606.962 o-ring size

Viton oring kit is avail from fryerpower.com

92497pmu · #9 10-11-2009, 07:03 PM

nagging problem of rough idle, excessive noise, vibration at idle - solved last month by a local independent mechanic.

Johnny Everett replaced my motor mounts (worn or broken, not really sure) and the benz runs great now. I guess there is a TSB for this and he had another MB in the shop recently with the same problem.

About $400 total for all parts and labor. Not bad considering it was pouring rain outside and nice and dry in his shop. He handed me the keys and was nearly giddy - "you won't even recognize your old car" he said.

I actually had to look at the tach to see that it had started - it ran so much better now! Actually a pleasure to drive again & just paid off as well!!