I notice what appears to be an adjusting screw (hex shaped shaft with a lock nut) on the rear top of the pump facing the firewall. Could adjusting this effect my rough idle problem? If so what is the adjustment procedure? If not what is this adjustment for?

I've had the car since new and doubt this adjusment has ever been touched. Car has 142K miles on it.

Thank you.

That screw is for setting the injection timing -- but I don't think incorrect injection timing will cause rough idle. Besides, you have to remove the vaccum pump to loosen the IP retaining bolts (the are inside the chain case).

Most likely cause of rough idle is bad engine mounts -- if the vibration is less in reverse and you can see the engine shaking, but it sounds OK, and loosening the injector lines one and a time doesn't sho a bad injector, replace the mounts. Don't forget the rear one under the transmission.

You could also run a bottle of RedLine or similar diesel treatment through it -- if the idle improves temporarily, suspect an injector. You may cure it is it is only a carboned up injector.

A long highway trip will also improve the idle quality, along with general running condition!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!