My car started fine when cold, and idled good when cold. As the engine warmed up the idle would start out OK but after a min or so, it would start missing a little and then after 2 min or so, it would have a "dead miss" on one cylender. Also when it was started after it was warmed up, it idled rough with this "dead miss". After you started moving, the problem went away until it idled for a short time again.
I found the problem by letting it idle until the miss started. I then turned off the engin and removed the plugs. One of the plugs was black and the rest were tan. The cylender that had the black plug was the one with the bad injector. When I tested the injector, it had a very slight leak. I tested it by removing it from the intake manifold with the fuel line still connected. I then put a jumper in place of the fuel pump relay so it would keep fuel pressure up. I then watched the injector and saw it drip very slowly. I swaped it with another one of the injectors and the the same injector still leaked. Swaping the injector with another one proved the problem was with the injector, and not the fuel distributor. I replaced the bad injector with a new one, started the engine, let it idle and the problem was gone. This whole process only took 15 to 20 min of my time. The injector only cost me $23.oo. Problem solved. Then and only then did I replace the other 7 injectors.
84 500 SEL (307,xxx miles)