My 83 240d has a miss and smokes a great deal. I have adjusted valves, corrected chain elongation which was 4 degrees, set ip timing to 24 btdc abd replaced the primer pump plunger. I suspect it has air leaking into the system. I put a clear hose from the feed line to the prefilter and saw no air. With a clear line as the return line, I see air bubbles periodically. When I pump the primer pump with the engine running, there is foamy air in the return line. The car starts easily and has good compression. It idles steadily, but for the miss. I would like to know any suggestions on how to isolate this problem.
thanks

 

If the engine is noticably missing at idle, crack one injector line loose at a time with the engine running and see which cylinder(s) the engine dosen't get worse on. Start checking from there it will probably be related to one or two cylinders. It could be injector lines, return line, or the injector itself. Good luck