take the injectors in to a place like Doctor Injector or similar for cleaning. It's like $32 an injector. If the misfires are happening afterwards, then I would do a leakdown test to check the head gasket. I say this because this is EXACTLY the process I did for my misfires. One injector was a little plugged, then the leakdown showed a leak between cylinders 4/6 on the HG. I ended up having thee bad exhaust valves too upon head disassembly. The logical reasoning I was told was the bad injector caused a bad air/fuel mixture which causes the exhaust valves to crack under the increased pressure load, which also screwed up the HG. So...injectors matter!