ok so i get my car back from being in the shop for 3 months, new engine harness (5k miles) and oil metering pump.. everything was fine but the mechanic at rotary performance told me i might need to replace my primary fuel injector in the rear housing.. heres why... first of all mechanic said he was driving at low rpms and then car started acting up.. miss firing, backfiring and so on..he said he pulled the plugs on the rear housing and leading plug was black as can be which means it was running rich (he had the plugs clean before road run).. he said he shut the car off and everything was fine afterwards.. now that im driving it i had the same prob happen.. i was on low rpms and car statrs misbehaving.. i rev up and once i go across 4k rpm and turbos kick in its all fine.. then i let it go to idle and its good.. as soon as i tap the gas it will start again and feels like there is too much fuel/not a good mixture air/fuel.. i have a primary and secondary injector that are in good shape, never installed or removed any before tho, any hints? is it easy to remove the injecteors, tell me what you guys think. thanks

Were the plugs replaced? That is what I would go ahead and do first so everything is easy. It would also help to check for trouble codes from the ECU.

Getting to any of the injectors on the FD is a big job. They're buried pretty deep. If it is a stuck or sticking injector, you could try fuel injector/system cleaner first. Of the over-the-counter fuel additives the only two I think are worth trying are Chevron-Techron (at double strength) and BG44K. BG is best, but more expensive.