Bought this car today. It idles rough. Glovebox paperwork showed an estimate for "rough idle" referring to a "weak cylinder". Suspect this means a ring job. However, from my "gasoline days" it sounds like it could be a vacuum leak. Any ideas?

Also, the heater & AC controls don't work, period. The blower doesn't even turn on when I press the controls. I checked the fuse, and it's fine. Is there a relay that controls the blower motor?

Many thanks! This car is incredibly clean! I will post pictures once I take delivery.

Congratulations on your purchase and welcome to MBshop. It idles rough cold and warm or just cold? Nope, vacuum leak won't cause that on a diesel, it'll just not shut the motor off. The climate control unit is a common problem, noticeable price to replace too. Somewhere around $300 I believe for a rebuilt one. Both my cars have had their fans quit from time to time, oddly enough in my 83 it seems like it always works correctly if I start the car with the fan going, but if I turn it on later it may or may not. I just don't pay it much attention, if it feels like working great, if not hey we all like a little time off don't we? I don't recall if it is relayed, but sometimes the brushes in the motor get weak.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

We just bought a 300TD, and the blower motor quit on me on the way home from the purchase! (in the rain, in rush hour.... ). We took the blower motor out to check the brushes, but it looks like the armiture is shot. I think most commonly it is a brush problem. There are brush repair kits on ebay. We bought a used blower motor at the auto wreckers. If you can find someone who is parting out a car, that might be an idea. I would try the blower first, before the climate control as it's cheaper, and very likely the source of the problem.

Good luck, and enjoy!

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Natalie

Congrats on the "new" Benz.

Just fyi, I bought some parts from a guy that posted in the "parts for sale" section here. His name is Rob, email address is Rlm1267@aol.com, and I know he has at least one '84 300Dturbo for parts, possibly more. Prices have been good and he ships what he promises - you might give him a try if you find that the blower motor is shot.

I had to replace my pushbutton unit. Rebuilt price was $180.70 with exchange of old one. ***Make sure that the auxilary (electric) water pump (engine compartment, on right fender down by the turbo) is working. If it's stuck it can cause some of the circuits on the above mentioned climate control unit in dash to fry.

Rough idle can be as simple as tired engine mounts or engine shocks.

Good luck! fmb

Thanks to all of you who have posted to my thread. I'm getting a lot of great information here!

In the meantime, I also purchased a 1982 300DT for parts. Is there a good bit of commonality between the 82 and 84? I "think" the 123 was basically the same between 1981 and 1984, but you folks know far more about this than I.

My rough idle was solved with a new Rack Dampener Pin installed on the back side of the injector pump. It is a spring-loaded pin that dampens out oscillations inside the injection pump that happen at idle. The original one gets weak with age.

A relatively simple replacement job. You should find pictures here in the forum if you search on "rack dampener".

My symptoms were a rough idle at stoplights - made the car shake side-to-side like a hot rod with a racing camshaft. (I also installed new motor mounts and engine shock absorbers, but the rack dampener pin was required to smooth the idle.)

Ken300D

You need to do a compression check to know for sure if you have a weak cylinder. As Ken said, on this model it very well could be the rack dampener screw that allows it to "romp."

A common cause for the climate control problem is the ignition switch. After starting the engine, wiggle the ignition key with the climate control set to full on and see if it comes alive. If so, the ignition switch is not too expensive and relatively quick and easy to replace. Don't buy a Climate Control Amplifier or any other part unless you have properly diagnosed and ensured that this is your problem.