You'll have a spare plug on the OM606.910. This spare plug is for the OM606.912/962 injection pump's rack position sensor which our .910 does not have.

The rack position actuator (red thing at the end of the IP) is controlled by the ELR relay (003 545 5205) located behind the battery on right hand drive cars but possibly reverse on US versions.

So, easy way to test for operation is to unplug the above relay and you will hear the revs drop or remove cross-over pipe and unplug the wire going to the back of the IP. Default idle is 570 RPM +~- 40RPM but if the control circuit is working correctly, the idle should come up to 630 RPM +~- 20 RPM the change is obvious but you must do the test with a warm engine 60-80C. The ELR controls a few other things such as AC clutch and temp sensor. Higher the temp, faster the revs to assist the water pump circulation when stationary.

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1995 E300 Diesel