2006 pontiac torrent. misfire and chugging.

[dluft1986]

I just bought an 06 Torrent with 1 3.4ltr engine. It is missing. Usually worse when first started. It runs down the highway ok but struggles in town. The codes are 305 and 405. Ive replaced the EGR valve, plugs and wires. It runs strong still just idles rough.

[carriedi]

you might try cleaning the injectors. a "motorvac" or something similar. the injectors will have a build up that can cause them to run lean and cause a slight misfire. Usually cleaning the injectors will improve the idle. a Motorvac disables the fuel system and runs a cleaner through the fuel rail and injectors. part of the process is just running the cleaner through with the engine off to work on debris in the rail and injector. the second part runs the cleaner in the intake and with the engine running. with the engine running the cleaner is injected into the engine and cleans the intake, back of the valves, piston top and then the exhaust. The misfire usually goes away for a couple of years and then it slowly creeps back and you clean it again.