hey derohanes,

1 i'm not sure 100% sure what could be caausing your missfire at warm idle, but for starters, i would suggest you keep it simple. i'm pretty sure that everyone on this forum will suggest that the first thing you should do is read/pull the codes. use the search option for more info, search for "w124 diagnostic trouble codes" and "blink code reader"(all the parts can be obtained at radio shack). then go from there .

2 as for witch hunter, i have not had any experience with them or their services, ask around, maybe someone from the peachparts forum knows of a good shop.

3 once all five of the fuel rail bolts are removed, disconnect the electrical plugs which go to each injector ,but leave the metal clips at the top of each injector on until you have pulled the entire fuel rail along with injectors from the intake manifold. the only thing keeping the fuel rail in the black plastic intake manifold are the fuel injector O-rings, so just pull up on each end of the fuel rail, and you'll eventually get it along with the injectors out of the plastic intake manifold.

then....

4 you can remove the metal clips which keep the fuel injectors on the fuel rail, all you have to do is pull on the injector to get it out of the fuel rail, the only thing keeping it in the fuel rail is a rubber O-ring, they are on there pretty tight though, so just twist and pull til you get em out.

ps. but before going to all this trouble, i would once again suggest that you pull the codes first

good luck