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idle adjusment 1984 300sd

Old 10-12-2017, 06:37 PM
Thread Starter
Join Date: Jul 2011
Posts: 32
Default idle adjusment 1984 300sd

The title says it. How do I adjust the idle on this car?
Old 10-12-2017, 06:48 PM
Join Date: May 2012
Posts: 2,125

Hello - take a look at the link below for the procedure.

Old 10-14-2017, 12:36 AM
Junior Member
Join Date: Oct 2017
Posts: 22

On the inner side on the injection pump, there is a vertical screw.
Loosen the 14mm jam nut and use a flat blade screwdriver to adjust speed. CW increase, CCW decrease.
Only snug the jam nut, it does not need to be very tight. Too much torque will break off the case boss and you will have to replace the injection pump.

RPM change will be small with adjustment, you might have to go more than a full turn just to increase speed by 100rpm. Idle should be 750rpm with the engine warm.
The injection pump automatically compensates for increased load at idle (such as power steering, AC and electric loads), so there is no need to set the idle above that. In fact if you set the idle too high and the engine runs above 1000rpm without a load it will enter the ungoverned range and revv itself to maximum speed (5400rpm).
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