Idle adjustment on 79' 300D

Between the injection pump and the engine you should see a tall screw with a lock nut. It's the idle stop and can be adjusted with a deep socket to loosen its lock nut and a large flat blade screwdriver to make the adjustment. Screwing in (clockwise) increases the idle speed, turning out decreases it. Keep a record of what you do so the original setting can be restored.

Thanks for the reply TG. If I could ask another question/opinion of you; About two month ago my 79' 300D (250K) started becoming "loud" at idle and at running speed. No unnormal tapping sounds just much louder (had the valves adjusted 3 months ago). Injectors were replaced 60K miles ago. The engine also seems to making a "chugging" sound and the idle has gotten higher. Performance is fine, no smoke and the head was removed and the valves were done at 220K. I had a mechanic check the exhaust system and it is fine. Any idea as to cause and/or cure?

Thanks, Toblin

It's difficult to diagnose a sound one can't hear but here goes.

A possible cause of "chugging" and a higher idle that comes to mind is injection timing. That includes the timing chain, camshaft timing vs. the crankshaft (crank should be no more than 5 degrees ahead of the cam) and the start of fuel injection delivery. I'd check the cam before the injection.

That said, you should know that the estimated useful life of these diesels, IMHO, is 250K to 300K miles. Unless your engine has had extraordinary maintenance, yours is at the threshold. The definitive test is a compression check which I'd suggest you have done before the winter for if the compression is falling you should know that the car will be marginal when the cold weather arrives.

You obviously like and care for this 24 year old car. If the compression test is bad news perhaps the car can be your "summer car" for there's no economic sense to rebuilding this non-turbo engine. Or, perhaps a used turbo diesel engine and transmission could be installed. That would solve the impending problem, if that's the case, and repower the car with an engine of nearly twice the power for less cost than an overhaul.

Tom