Before you mess with the linkage rods...

Adjust the base idle first.

#1. Be sure to have the hand vacuum pump connected to the shutoff valve before beginning this procedure.

I suggest using this tool for safety (none contact) and accuracy.
Digital Photo Sensor Tachometer
http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html
Accuracy resolution: At 1000 RPM or slower: 0.1 RPM , stores last minimum and maximum readings, auto-zero adjustment, detection distance: 1.97"-7.87" depending on ambient light, 5-digit LCD display, Includes case and reflective tape, runs on four AA batteries.

Factory Service Manual calls for:
* engine temperature 60° - 80° C for idle adjustment.
* idle 700 - 800 RPM
* maximum no-load 4900 - 5200 RPM

#2. Remove the linkage rod to the injection pump.

The real idle adjustment screw/spring pin.

#3. Between the engine block and IP there is a mounting ear cast into the injection pump body. Screwed into the mounting ear there is a vertical tall round rod with a large flat blade screw slot, It has a 14 MM locking nut at the base, loosen it.

#4. Unscrew and remove the idle screw/spring pin.

#5. Clean the threads, making sure the nut moves easy through the full length of the threads.
Note: The locking should be as high up the the idle adjustment screw/spring pin as threads allow.

#6. The screw/pin has a spring loaded rod in the bottom = it must be lubricated and move easy through the full length of travel.

Install:

#7. Install the idle adjustment screw/spring pin roughly 1/3 of the thread depth.
* Deeper = faster engine idle speed.

#8. Stand ready to adjust the idle adjustment screw/spring pin and have someone else start the engine.
Note: The engine idle will be so low it may not start, try screwing it in three turns each time until it stays running.
* Deeper = faster engine idle speed.

#9. Have your assistant use the tachometer on the crankshaft harmonic balancer (calling RPM) while you do the fine adjustment.

#10. Install the linkage rod to the injection pump, if the rods are adjusted correctly there should be no change of base idle RPM.

#11. Turn off the engine, if it fails to shutdown, back off the idle fifty RPM and try again, stop when you are satisfied with the results.

#12. Tighten the 14 MM lock nut to 15 NM = 11.06342 lb ft.

#13. With the engine off, punch the accelerator to the floor hard three times and let off, Re-start the engine and Repeat #11.

#14. If it starts, idles within specification, and shuts-down = you are finished with this DIY.





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Excellent, thank you. I need to adjust my idle . . maybe this gives me a reason to buy another cool tool.

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

The real idle adjustment is inside of the IP. It is controlled by a governor and that adjustment needs to be done on a machine.

Technically correct, however this DIY covers the EXTERNAL base idle set screw/spring pin = the one you don't need a half million dollar machine to adjust.

Rebuilding injection pump
http://www.peachparts.com/shopforum/showthread.php?t=248014

There ought to be a warning in that procedure regarding the 14mm locknut.

The locknut can take way more torque than the aluminum mounting ear can withstand. Exceed the capability of the mounting ear............and you break it off the IP............before the nut even moves.

Attempting this procedure is DANGEROUS.

Failure means the IP has to be replaced.

I am 99.99% sure that I MUST HAVE one of those tachometers now

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$110 OM606 Blank Exhaust Flanges
No merc at the moment

Recycled for new owners

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For owners of om615 220d vehicles (and perhaps other w115 diesels), because there is a throttle and venturi at the entrance to the intake manifold, we can adjust the idle there. There is a small screw that can be turned to adjust the idle. This is even easier than the procedure described in this thread.

If, for whatever reason, you don't like easy solutions, you can also open up the injection pump and install shims at the diaphragm. The FSM says how much the idle will change per amount of shim.

__________________
1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Thanks for "recycling" this thread! I just sat down to search for information about this adjustment. My idle has been too low since I bought the car. I bought the HF Digital Photo Sensor Tachometer and found that it is running at 540-560 rpm. My big question before actually starting this procedure concerned what exactly was under the screw and could it be removed for cleaning. Your "most excellent" DIY answered all my questions.

Thanks again!

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Baton Rouge, LA
1977 300D Non-Turbo

As an option to the HF tach (which I'm sure is more than adequate for this adjustment) look up "Monarch Photo Tach" on Google and go to their website. I needed a dash-mounted tach for the race truck and we used the Monarch units in our permanent dyno instrumentation so I was familiar with them. It was one of the pieces of instrumentation that we never had to second guess. They work great and can have stupid levels of accuracy though I opted for 1 pulse/rev - you just tell them how many pulses/rev you want and install as many pieces of shiny tape as you need. They'll set up the signal processor/readout for the number of pulses you specify.

Anyhow, I think I paid $240 or so for my Monarch but it IS designed for panel mounting. Just an option.......

Dan

Gents - This was an excellent DIY tutorial. And yes - a little scary removing the 14mm nut - had even added liquid wrench prior.

Owe you big - saved me a lot from going to the dealer.

I saw similar idle - 500 rpm and when the A/C kicked on was afraid the motor mounts would shear. Experienced this low idle after a dealer A Maintenance Service.

Anyone know what the RPM should be w/AC on?

Want to keep my Panzer to 1 million.

Thanks for this, an easy job but intimidating. I have an OM617 swapped 240D that has a lot of vibration at idle, I've done a lot to chase it down, many diesel purges/filter changes over the past two years, and a valve adjustment, and most recently - a new rack damper. I adjusted the new RD basically all the way in to smooth the car out, it worked well but it seemed to have a little "bounce" when letting off after full throttle and the starting was a bit harder than normal, so I figured the adjustment was too far in. I backed it out and the "bounce" is gone, and it's a bit smoother than before I replaced the RD, but it's not as smooth as it was with the RD all the way in.

I figured the next step is adjusting the base idle, so I turned that up a bit before I had an optical tach to measure. Once I got one, I took some measurements at the crank. It was 750-780 at 80 degrees C engine temp with A/C on high, and 830-850 with no A/C so I turned it down to 800, as base idle, 80 degrees C engine temp with no A/C.

I have read that base idle should be 700-800. After driving around 10 miles in city driving, I measured the idle again, it was 875 with A/C on full and 900 with it off. Is this within spec?

Here are the measurements I took in its current setting (am using a cheap tool so a good part of the variance could be the tool itself):

Base idle at 80 degrees engine temp with no A/C: 800
Idle at around 90 degrees engine temp with no A/C: 900
Idle at around 90 degrees engine temp with A/C on full: 875

The shaking with the A/C on full is livable but not ideal. It feels like the car wants 50 revs more or so to be smooth with the A/C on. Should I increase my base idle speed at 80 degrees engine temp to 850? Is there any danger of triggering a run-away or anything like that? It just seems like the car would be happier with a bit higher idle.

What difference does it make ,just stay a couple hundred rpm below run away speed in neutral or park. None Of the Dealers back than had tachs.
How did they do this; increase rpm slowly intill engine speed increases by self,that"s
breakaway speed,release throttle,let idle,do again just to be sure,stay a good bit back from this speed. Engine must be fully warmed up. Yes ck. throttle linkages first.

So an increase of 50 RPM makes no difference and is safe in your opinion, hercules?

Only done a few hundred. No mishaps,just stay away from break away speed.
Set idle,than see how far away is breakaway speed,if a good distance in rpm, that"s
it. 50 rpm increase from factory set should not be a problem,but always check your
breakaway setting.