1981 240D Idling rougher after valve adjustment

Before valve adjustment, car idled fine. Immediately after valve adjustment car idled fine. Probably after 1,000 miles of driving, car idles rough at a stop in drive or in reverse but idles fine in park. Another change is that it has gotten cold. This was a florida car and not used to the cold. I did install a block heater from you which helped with cold starts.Turning the idle adjustment knob on the dash to the left increases RPM and helps idling.

1.How do I adjust the idle so it will run right again without having to adjust the idle knob on the dash?
2. Is it ok to drive the car with the idle adjustment knob turned to the left a little bit?
3. Would fuel delivery have anything to do with this? Just ordered from you some fuel return line as mine are leaking. I think fuel filters are due also so I ordered some of those from you also. Love the car and really want her running right again. Thank you for your help!

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Diesel Engine Specific Aid

Chassis Model Number

W123

1981 240D Idling rougher after valve adjustment

unless your return lines are gratuitously squirting fuel at idle, they shouldn't affect the idle to the extent that you are describing. Those lines commonly leak a little and when you catch it, it's best to replace them as you plan to.

The idle knob only affects the idle speed. it raises or lowers the "bottoming out" position of your throttle linkage. when you turn it up its like pressing on the gas (diesel) pedal a little bit for you so you don't have to ... so it's ok to drive the car with whatever idle setting you have.

as far as the valve adjustment, what were the clearances like when you adjusted them? did you notice that any of them were particularly loose or tight? reason for asking, if some were really tight and some pretty good then a scenario as follows is possible:
the good valved cylinders are running just as they were.
the tight or no clearance valves had a nice little layer of carbon build up that would seal the valve between the valve sealing surface and cyl. head. now that you've made proper clearance, that carbon has been "smashed away" and your clearance is tight again and/or you're not sealing fully once the engine is warm. does that make any sense?

now that it has been 1000 miles, check the valve clearances again.

1981 240D Idlling rougher after valve adjustment

Thank you for your reply. I understand what you are explaining and it makes sense. When I did the valve adjustment, all clearances were tight. I will go back now after the 1000 miles+ has been driven and check the clearances again. Thank you.

Idle Adjustment

I would recommend you get my Diesel Advanced Fault Diagnostic manual. There are a number of things that could be causing your problem.

1. Do a repeat valve adjustment as per reasons stated above
2. What about condition of injectors? Have they been removed, cleaned and inspected.
3. Do a Diesel Purge and THEN change your fuel filters.
4. Have you done a compression test?

It is normal to turn the knob up when cold. It is just fine to leave the knob in any position. Once the engine gets real hot you should be able to turn it down. If you can't it means something is not right when engine tuning as listed above. Only adjust the idle stop as a last ditch measure for a tired engine.

Hope that helps, Kent Bergsma.