2002 Gmc 5.3l

[PoorboyVortec5.3]

My 2002 GMC Seirra with the 5.3l (110,000)has a weird rough idle. It shutters or shakes at idle. The RPM's are at 500, but it has a shake that goes in an out. This seems to get worse as the truck gets warm. I got a SES code for a misfire in cylinder 3 and Here is the run down I have changed the plugs and the wires, fuel filter, air cleaner and cleaned the throttle body and MAF. I also have been running Techron in the gas to get rid of the problem. No luck. So I took it to the dealer and they said it was bad/dirty injectors and put injector cleaner in the tank to see if it would help. I haven't checked the fuel pressure at the rail yet. Any help would be great.

[coiler_1061]

mine had a similar problem, my mechanic discovered that the intake plenum is damaged at the base and causing a small vacuum leak which could cause issues like yours.