87 300SDL Rough idle issue
 

When the car is in drive it starts to idle a little rough. The same goes when you put it in reverse. When in park or neutral is runs smooth. Also when accelerating it runs fine, this only happens at idle. The quick fix has been to clean the wires that connect to the injection pump, and that fixes it for a day or two. Noticed that the hard metal fuel lines that deliver fuel to the injectors are wet on the pump end. Not too familiar with this but i have read something about some o rings that go bad and let air in. Not sure if that is what is happening, or if there are other issues

It could just be that when in Drive or reverse the idle is dropping to a point where it just shakes more. You could always turn up the idle a notch or two with the black knob in the engine compartment (drivers side near brake booster). Its a black dial about 1" diameter with the numbers 1-7 around it. I believe each notch will increase/decrease idle by 20rpm or so.

Definitely need to fix the fuel leak though. There are the 6 o-rings in the IP. Pretty easy to replace (DIY posted before). Use Viton if using Biodiesel

Let us know what fixes it once you find out.

I will definatley replace the rings on the IP. I dont think its because the rpms drop. This happens randomly it will idle smooth and then rought, like its missing or not getting fuel for a second the smoothes out again. My guess is that it is sucking in air. I will try the seals on the IP and see if that helps. I am also thinking that the leak is getting the connection on the IP wet and causing a bad signal to the ip, because when I clean the connection on the IP it will be fine for a day or two.

Roughness may be caused by weak left hand side (drivers) engine mount. The fuel leaks on the IP will contribute to this as the fuel softens the rubber in the mount.

can someone refer me to the DIY. I tried searching but cant find it.

The phrase delivery valves should bring up ton of posts in the archives. Or delivery valve seals if it does not. They could easily cause this.

Fuel oil is not conductive to the best of my knowledge. For example large transformers can use oil as the heat transfer medium. It is a little strange that those connections seem to act up on the injection pump every few days.