I have been chasing a rough idle in my 1979 240d for the past several months. Here is what has been done so far.
1. Fuel tank removed and flushed.
2. All rubber fuel lines replaced from tank to fuel pump.
3. New pre-filter and fuel filter (additionally running a racor R12T 10 micron filter.)
4. Rubber lines between injectors replaced.
5. Idle adjuster cable replaced.
6. O-ring and copper washer replaced on fuel filter bolt.
7. Yesterday I had Bosio nozzles installed and adjusted by a professional locally. He set them to 117 bar as he said that they will settle to 115. He also showed me the spray pattern of each injector.
8. I have been running Stanadyne fuel additive through the tank.
9. I have taken apart most of the throttle linkage and cleaned and lubed it.
10. Fuel pump was rebuild by previous owner at a shop.
Most of the time in park and neutral the car idles fine and doesn't shake. One strange thing is that sometimes it idles up by itself. You have to rev it up for it to drop back to regular idle. The biggest problem is whenever the car is put into reverse or drive, the idles drops and the car begins to shake severely. I am stuck and don't know what else to do. Please help.

When was the last valve adjustment done?

When you say fuel pump, do mean the lift pump or the injection pump? New primer pump?

Do you have new motor mounts and trans mount?

How does the throttle pivot bushing look like on the firewall?

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The last valve adjustment was done less than 500 miles ago.

The injection pump. I have no other information as to what was done to it.

I know the motor mounts were replaced. Not sure about the transmission mount. Will check.

I dont have a throttle pivot bushing on my vehicle.

What is your idle speed?

If you put in gear and the engine doesn't run smoothly, a small increase in the idle speed usually helps.

Check and adjust the injection timing.

How Long ago was the Fuel Injection Pump Rebuilt and how Many Miles are on the Engine?

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84 300D, 82 Volvo 244Gl Diesel

Carefully examine if air is in the fuel supply. Possibly the best way is to put the return line from the injection pump in a jar submerging the hose end. Running the engine and watching for air bubbles in the fuel. Sometimes you may observe a small stream of bubbles transitioning through the pre filter as well. Air content in the fuel can upset the idle as well.

I have no way of telling what my idle speed is as I dont have a tachometer. I have adjusted my idle speed on the injection pump by ear but that is as close as it gets. I would love to know what rpm the om616 is supposed to idle at.

When I am driving I usually crank the idle speed using the cable on the dash, at higher rpm's it runs fine but when I stop at a stop light I have to put it in neutral because it shakes so bad.

By injector timing do you mean the start of fuel delivery?

When I bought the vehicle the owner said that the fuel injection pump was just rebuilt. I bought the vehicle December 2011, so a little more than a year ago. The engine has 225,000 plus miles.

There does not seem to be any air bubbles. At first I also though that air was entering the fuel so I replaced all rubber fuel lines, any o-rings or washers that I could. There is no stream of bubbles going through the prefilter, although I have noticed that my prefilter does not fill up all the way and there is an air bubble at the top. I have attached pictures to show what it looks like. Is this normal? Also I am wondering if my racor filter is causing a fuel flow problem as I don't have any type of electric fuel pump to aid in fuel delivery. When I hooked up the racor filter I used a handheld vacuum pump to suck fuel through it and then connected the line to the primer pump. I also disconnected the return line and put it in a jar filled halfway with diesel and there was no air bubbles.

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I'll chime in with personal experience chasing air in fuel problems.

"off the rack" copper washers don't seal the same a as MB "sealing rings"

I had put all new copper washers in mine still to be troubled by air

Pulled all the original sealing rings off at a JY and replaced the copper and solved the air problem.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Interesting. I got the copper washers at a local shop that works on European imports. I have a parts car that I will pull the washers oof and see if it makes a difference. Thank you.

How's the blow by on the engine?

Ever did a compression check?

Anyone use any alternative fuel?

May have to face the facts, that your engine is worn.....both my cars ran with a rough idle due to poor maintenance from the previous owner....my current one, idles rough and I hate it but I have bad blow by...so nothing I can really do...

I would remove the third filter, just my personal preference....if anything I would install a water fuel separator..

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The OM616 idles between 700-800 rpm. First you set it with a warm engine (not hot, but warm) in neutral/park and without the A/C. Idle speed adjuster not engaged. Closer to 800 rpm is generally better. After that you engage a gear and put on the A/C and adjust a bit so that the engine runs smoothly.

A optical tachometer is not very expensive.

So the engine also shakes if you increase the idle speed with the idle adjuster screw?

It could be a problem with the transmission, as the shaking only occurs when the transmission is in gear. Did you adjust the linkage according to the FSM? The adjustment of the transmission rod is very important.

I think I need to figure out my rpm's. Is an optical tachometer the only way, if so any source to where I can buy one. My parts store can't even order one.

With the idle screw turned all the way counterclockwide it doesnt shake but the rpm's are too high.

I looked through my online mercedes manual but it doesnt even have a section for transmissions. Guess I need another source.

On My Car there is an Emission Sticker and part of the info on it is the Idle Speed. The sticker with the info is on top of the Front Upper Crossmember in front of the Radiator.

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84 300D, 82 Volvo 244Gl Diesel