My 84 240 DL wagon's engine has started idling rough. When i give it some gas, the roughness is not noticable. It is an even roughness, not random. The car does not feel like it wants to die, it is just running rough, and the car vibrates because of it at idle. I want to say it feels like it is missing, but that is just a guess. I have checked for spark at all the plugs and I've got spark to all 4 plugs. I also checked the air filter and it looks OK: not too dirty. What should I do next? I know I should pull the plugs, but since they are less than one year old, I doubt they are that bad. Assuming they look OK, what should I check next? My thought was maybe one of the fuel injectors is screwed up. How can I check the injectors? Any advice is appreciated.