My glow plug light flashes sometimes maybe ten times after starting. It never has seemed to be an issue. A shop testing the plugs as being ok but tried to sell me an overpriced glow plug relay. If I am starting ok, should I try to find one of these or am I ok?

I also still cannot solve my issue of rather rough idle when in drive with the breaks applied. Can get rather rough at long lights.

Any thoughts?

Thanks. Mine is a 1980 300SD.
I believe the manual idle control is not on mine but is on any older ones. I wish it was now!

Is there an idle screw anywhere I can easily get at?

You might check the threads about the replacement rack dampner screw. It is located on the rear of the IP and is right in front of the oil filter. Ir it has not been replaced it will need to be. I believe the replacement is gold, and the original is silver colored.
There are several threads giving better advise than I could here about setting it, but if it is not set right, that will cause an idle shake. But then, so will several other things. First things first.

I have done mounts and it made a big difference so somehow this rack dampener bolt is making sense.

Is this a big deal to replace considering I have no idea where to start. Don't even know where my injector pump is. Can someone help point me to the screw so I can tell whether or not it is the original one?

The injector pump is on the left side of the engine. Just follow those tubes from the injectors to it. It is about the size of a football. The oil filter is mounted directly behind it.
On the rear of the injection pump is a bolt with a nut threaded on it. Sits a in a very tight spot between the oil filter and the injection pump.( The bolt points to the rear.)
If it is gold tone, then it may just require adjustment. Better search the threads for the best way to do that, but if memory serves you loosen the bolt and tighteing nut and then turn the bolt in until the engine smooth out. If it is turned in too far the engine will stall when you try to go. Just turn it back a little.
If it is silver tone then you should replace it. Those were the original and they have been faulty.