The injectors can be a real bear to get out of the intake manifold and you can break the plastic nose piece doing so. I would definitely not soak the injectors in parts dip, that stuff melts plastic and the injectors are part plastic. A shop doing the $70 or whatever cleaning might do some good, however what I would do (which I haven't had to do yet myself so I make no gaurantees) as others on this board have recomended is dump some alcohol in the gas. It would tend to lean it out which might increase nox but it also burns cooler which lowers it and if you get it lean enough nox goes down anyway. So, I would try alcohol with a pretest just in case it is worse. Good luck, Mike W.