I am fairly new to Diesels. I have a 1983 300SD and it idles pretty ruff. It also clacks loudly at idle and up to about 2000 rpm. The car is great, 192K and runs like a watch. When I am up at cruising speed (70-80) it is as smooth as silk. When I am on the street and come to a traffic light it idles ruff ( I can see my hood doing a jig) and is fairly loud (clackty clack) especially when I have the windows down (California guy). It idles, according to my tac, at about 700-750 rpm.

I had the valves adjusted (which it needed) but didn’t help. Since I am new I don’t know if there is any type of adjustment or tuning I can do to smooth things out or quite things down.

Any suggestions/comments?

Have your engine mounts checked, often these will cause the motor to be lively, if they are original, they most likely are flat. Parts are cheap, installation depends on how easy they come out. What weight oil do you use? And, do you have a hoodpad that is still functional? The noise you hear could be normal diesel clatter...depends opn what you're used to....compare to other 300SD's or 300D's to be sure.
-Larry

Yeah, I have a friend that has a '87 SD and his is quiet as a church mouse compared to mine. I checked my hood pad and it looks good but I will replace it just because.

I also failed to mention that I replaced all the fuel filters and ran lubro molly purge through the system and put a can of lubro molly cleaner in a tank of fuel to clean my injectors. I use Marvel Mystery Oil (8 oz) in every tank also. The other thing is I'm only getting about 20 mpg with street/highway driving.

Apples and Oranges
 

Clancy,
Your friends diesel and yours are quite a bit different. You have 5 cylinders and he has six cylinders for starters...not to mention he never has to worry about adjusting his valves either. Look for 300's at gas stations or parking lots, and give them a listen.
-Larry

Maybe you have some air in the fuel system. Do any of your braided hoses look moist, or is your fuel pump hand pump leaking? I just rid my fuel system of the air leaks and it really quieted the engine down.

Thanks Patsy, what is the best way to purge air from the system?

I did replace all the hoses that jump from injector to injector because one was leaking and it was cheap to replace all of them. I think they are the back flow or over flow hoses.

See if you can locate your hand pump. It is mounted on top of the fuel pump. The fuel pump is mounted to the side of the injection pump. You may have a white cap, or a black cylinder. If it is black, push down on it, and that is how you pump the air out of the fuel system. If it is white, you have to unscrew the top and then pump. The white is the old style, and they are prone to leaking. I don't know what year they switched to the black style.

You may want to crack a union screw on top of the main fuel filter, and pump until no air comes out, keep pumping while you tighten the union nut. Make sure it is the union nut, after the filter. This is supposed to be done each time the main fuel filter is changed.

If you don't crack the nut, I think pumping 20-30 times will get the the air out. You should hear an audible rattling coming from the engine side of the injection pump.

This is how I do it, others may have a different idea.

Thanks Patsy, I'll try that this weekend. My hand pump is black with a large flat white plastic screw nut at the top.

I don't know if that unscrews or is ready to pump, hopefully someone else with your year will chime in. That description does not ring a bell.

Patsy,

Another question. When I replaced both the fuel filters the small clear pre-filter has air in it. I can see an air bubble about a half inch in diameter at the top of the filter and it doesn't go away. Could this be causing me problem or is it normal?

I have read here that the air in the prefilter is normal. I have tried to get rid of it myself. I don't think it causes any problems. Do you have a glove box owners manual? I think your hand pump is mentioned in there. If you run out of gas, you are supposed to pump the hand pump after you fill up, so they talk about that in the manual.