I have been chasing a rough idle in my 1979 240d for the past several months. Here is what has been done so far.
1. Fuel tank removed and flushed.
2. All rubber fuel lines replaced from tank to fuel pump.
3. New pre-filter and fuel filter (additionally running a racor R12T 10 micron filter.)
4. Rubber lines between injectors replaced.
5. Idle adjuster cable replaced.
6. O-ring and copper washer replaced on fuel filter bolt.
7. Yesterday I had Bosio nozzles installed and adjusted by a professional locally. He set them to 117 bar as he said that they will settle to 115. He also showed me the spray pattern of each injector.
8. I have been running Stanadyne fuel additive through the tank.
9. I have taken apart most of the throttle linkage and cleaned and lubed it.
10. Fuel pump was rebuild by previous owner at a shop.
Most of the time in park and neutral the car idles fine and doesn't shake. One strange thing is that sometimes it idles up by itself. You have to rev it up for it to drop back to regular idle. The biggest problem is whenever the car is put into reverse or drive, the idles drops and the car begins to shake severely. I am stuck and don't know what else to do. Please help.