i have noticed that my w123 300d has idle shake if i am in D/R/S/L but if i shift into neutral the shaking goes away. As the car gets warmer the idle gets more smooth as well (but still a shake). I was thinking about changing the transmission fluid and filter (it's been ~20000 mi) but was wondering what would be the most likely cause of this?

Thanks.

Definitely change the transmission fluid but that probably won't alter the shaking - have a look at your engine mounts.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

engine mounts were just replaced. (2 weeks ago). It was shaking before that. The weird part is that if it's "in gear" it shakes at idle but not in gear it's ok.

That's hardly a weird thing - certain parts of the transmission are gripped by bands and clutches when it is in gear so the engine is under load. That doesn't mean it should shake in gear though.

Were the engine shock absorbers re-fitted / replaced along with the engine mounts?

Have you checked the engine idle speed?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

shaking too,can be a fuel problem too,clogged primary filter or tank screen.Also if it has original screw rack damper the spring gets weak.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Or it could be a weak cylinder. These things are always more noticeable when the engine begins to pull against a load.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Too many possibles. Start from basics.

A rough idle on our diesels, particularly our stone-age 5-cylinders, is easy to diagnose.

Most common is air in the fuel injection system. You have fresh fuel and fuel filters. Is the fuel visible in your primary filter clear? Is the fuel system well bled of air? First bleed at the outlet banjo bolt on the secondary filter. If still rough, bleed at each fuel injection hard line at the injector end. If that doesn't fix it, move on to ....

The next most common is valve adjustment. Should be done every 12000 miles if pre-1981 or 15000 miles on later.

If still shaky, look at your engine and transmission mounts even though they are "new". The engine shock only comes into play at engine shutdown.

Don't concern yourself too much about in gear/out of gear. The difference there is load/no load which will make a rough idle seem worse. The possibility of an internal transmission problem causing it is there but really remote.

My bet is on air in the fuel injection system.

But what do I know.

A new rack damper screw helped mine out, back in the day. (although what really smoothed out the idle, was a gal. of veg oil).
If you have a female passenger, and the car shakes, look at their chest...it will take your mind off of the shaking - once you hear car horns blaring, you know the light turned green and it's time to go.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

1. motor and trans mounts look fine (are band new) and seem solid.

2. just replaced all fluids and filters. I did not replace the rear tank screen filter .. but this is a wagon so the fuel line does not directly come from that filter.

3. fuel was dark before i replaced all fluids and filters. Now it is much lighter but not quite as light as it should be. This could potentially be part of the issue.

4. did a valve adjustment last week with 2 cans of diesel purge after (that's when i replaced all the filters)

5. replaced all rubber lines in the engine bay for fuel delivery.

6.i replaced the primer pump and seal.

7. I don't see any bubbles in the lines but i did not bleed the banjos.


in gear i feel it ... out of gear... no problems.

While running, in gear, with someone standing on the brake, you can crack one injector line at a time, and see if the idle changes, if one of the cracked lines does not cause a change in idle, then you can start being suspicious of an injector.

__________________
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Autos have a higher idle RPM to allow for the fact that under load (ie putting into drive) the revs will drop...seems like yours could need bumping up a bit.

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

this guys got it right. i spent weeks chasing rough adle, and all it took was a couple turns in on the idle adjust screw. bump your idle up a bit to compensate for the load of being in gear. it takes 2 minutes and youll be blown away.

I've also got some rough idling...

Would 90,000 miles on a rack damper screw be reason to replace it (spring in there weakening)?
This is for my 617.952 (300CD-T).

I think that not only miles, but time itself, can have an effect on a spring. Try adjusting it first, before opening your wallet up.

__________________
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

i have increased idle screw and a lot of the shaking went away.

2 questions..

1. how can i tell what my rpm is?

2. how do i tell if i want to increase the idle or the damper.. Which is more preferable and it seems like i can do either to fix the problem. Not sure which is preferred or correct procedure to figure out which one to do? (how much of each).