It's been a couple of years now that my 82 240D with approx. 240K miles has a rough idle problem which manifests mostly after a long drive. It got to the point where the engine would start to stumble. It then progressed into a shuddering upon acceleration but smooths out at around 45 mph. I did a diesel purge a couple of weeks ago but only used one bottle. The leftover purge was quite dirty with some pieces of floating debris. I changed the fuel filters immediately post purge. The shuddering and stumbling improved visibly but are still there. There is no excessive smoking, fuel filters have been changed regularly and car runs fine otherwise. I have noticed over the past couple of weeks that the car takes a few seconds of cranking to start. Starting used to be immediate. Does all this point to an injector problem or could something else be amiss?