I'm trying to get my 240D into tip-top factory new shape but unfortunately I don't have a base-line as to what perfect is. I've researched rough idle conditions but I don't know just how smooth it should be - 100% ideal. Basically I don't know what normal is supposed to be.

Idle is def rougher when cold. You can see the steering wheel vibrate and the air filter definitely moves a lot. When warm there is absolutely no vibration when in park or neutral and the vibration is much better in Drive than it is when cold. Turning up the idle adjustment does cure it but leaving it there causes harder shifting. I know a diesel is going to be rougher than a gasser but just how much should I feel.

What I've Done that may relate to possible rough idle:
New engine mounts
New Engine T mount
New tranny Mount
New engine shock
New fuel filters
Valves adjusted and then double checked
Rechecked torque on all mounts
Engine was a new crate engine 50K ago
All new MO1 fluids
New air filter
Plus a trillion other things unrelated to possible issue.

Sorry for the sort of vague question.

Thanks,
-T-

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'83 240D

GLOW PLUGS

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Moss Gate Bed & Breakfast
1985 300 TD GG done in by a red light runner
1984 300 CD Sold
2008 Titian
2000 Cadillac SLS
1966 FLH Sold
2003 Harley Ultra

Only practical thing I can think of is side by side comparison with a good 240d. It is just too subjective unless you were working on many cars of this model every week.

The fundementals of a crate engine with 50k. Especially if delivered with a new or rebuilt injection pump should still be good. You just may have the idle too low when cold. For starters you can read the idle with a cheap electronic hand held tach these days. You might also be able to adjust the automatic a little.

Sorry, forgot glow plugs are new as well (less than 2K on them).

I'm trying to find an early 300 tach to put in. I've already got the leads from the egr computer all ready for it.... just have to find it.

Maybe this is a better question- how should an ideal 240D idle compare to that of a w124 300 diesel? Even in the same ballpark?

Thanks,
-T-

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'83 240D

6 cyl is smoother than 4... new smoother than old. etc...
still. i hear the 240's are smooth.
if it's a cold thing, I'd start looking for air leaks, and VERIFY the compression, and the Glow plugs are good. then RE balance the injectors if they've been done.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

One question. What do you mean by engine shock? The 240D's did not have engine shock absorbers from what I've read and been told by numerous MB mechanics. Mine certainly didn't and it idled incredibly smoothely, though I didn't have the idle speed knob turned down all the way. It was probably about a quarter turn from it's slowest position. I did notice though after I had changed my engine and tranny mounts that there was a noticable side to side wiggle from the car that was not there before. Part of the reason I increased the idle speed slightly to remove it. But I would say that all things being equal a 240D should idle extremely smoothely. Much more so than you might expect from a diesel four banger.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Sweet,

Thanks for the info you guys.. I was beginning to think I was on a quest for the unobtainable. Seriously, much appreciated!

Compression is good the only uncertainty I have is injectors but was beginning to think I was on a wild goose chase. I figure I'll give the Monarks a try and see where I am after that. And also accurately check where the idle is set and out a meter on the GPs.

Yes my 240D has an engine shock - It's on the left / drivers mount arm. OE was a stabilus and I replaced it with a Bilstein and Genuine engine and engine shock mounts.

The engine shock is small, about 6" long and about 3/4" diameter if I remember correctly.

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'83 240D

The best description I can give in written words as to how it SHOULD sound is that it should be EVEN pulses. A properly running diesel of most any description or brand should idle with a very even series of pulses. If not, then there's something wrong.

On my 79 automatic the idle is a little rough. I tried everything you did. The last thing I have to do is to check injector preasure and spray patern. I think that at lower RPM at stand still the injectors need a look at. It runs great and once you give it a tad of fuel, it is beautiful. We'll see.

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1979 240D Caledonia Green/cream gone
1982 240D stick Ivory/Palimino
1999 E300D White/grey

Yeah, That's about the same as mine. Sounds great and runs awesome but I just can't get rid of the shake without kicking up the idle. I've replaced virtually everything on the car (a 5 page list in fact) and am getting ready to sell a kidney so I can get it repainted. The idle's the only thing bugging me and I really doubted injectors would be bad after 50K. After all the work I was going to replace the injectors in the relatively near future anyway but I guess it just got bumped up on the list.

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'83 240D

If I actually kick up the idle with the dash thumb screw, it is fine. Until I have to shift from neutral to reverse and it bumps into gear. Then it spills my coffee and that isn't good.

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1979 240D Caledonia Green/cream gone
1982 240D stick Ivory/Palimino
1999 E300D White/grey

I have a worn out 616 four with low compression. It barely starts when its cold out but purrs like a kitten when started.
When it warms up you can set a glass of water on the valve cover.

It runs smoother than my wife's low mileage 617.

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Experience : what you receive 3 seconds after you really needed it !!



86 300SDL 387,000? Motor committed suicide
81 300SD 214,000 "new" 132,000 motor
83 300SD 212,000 parts car
83 300SD 147,000

91 F700 5.9 cummins 5spd eaton 298,000
66 AMC rambler American 2dr auto 108,000
95 Chevy 3/4 ton auto 160,000
03 Toyota 4runner 180,000 wifes

Engine shock absorbers are mostly for when the engine is being stopped. The motor tends to "kick back" because of compression, and the shock absorber is supposed to reduce the shaking on shutdown. They don't do anything for the idle.

My 300D had both shocks missing. I bought and installed the mounts (because they were gone too) and the absorbers. Not cheap. I do not think they do anything, and next time I would not bother with the engine shock absorbers.

My 240D has no engine shocks and nowhere to mount them, and I don't miss them.

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'82 300D (project)
'46 Willys (project)
"Nothing seems to be the way it should in this garage." -jt20
"Smarter than an engine, dumber than a hoodlatch..." -jt20
"Start jumping up and down to smoosh down those engine mounts" -DeliveryValve
"no" -kerry
"At this rate, you may have it done by winter" -layback40

My 240D W115 idles smooth with a faint vibration.

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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

My 81 is smooth with slight vibe but the 82 shakes like a racehorse!

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1981 240D 143k 4 spd manual -SOLD

2004 VW Jetta TDI 5 speed 300k -still driven daily