2005 Suburban Idle Problems

[cconaf2]

I am trying to fix my friends 05, suburban 1500, 5.3L. It has 63,000 miles, and idles rough. I ran the codes and got P0300, multi cylinder misfires. They changed the wires and plugs about a year and half ago due to a rodent eating some of the wires, but they were having the idle problem before that. There sounds like a vac leak but I sprayed carb cleaner around the intake gasket, and hoses but the eng did not increase. I pulled the air intake and could see the butterfly valve pulsating and tried spraying cleaner in it but the eng almost stalled instead of reving up...Thank you,

[txab]

Cleaned the MAF? Checked fuel pressure? It still can be intake gaskets, since they are known for leaking.. If you're going to clean the throttle body do it while the engine is off.

[gmtech]

Intake gaskets and or trash in the fuel rail. Its really tricky to locate the intake gaskets, they leak on the bottom side and the foam inserts on the bottom of the intake make it hard to get anything sprayed in there. What do the fuel trims look like?

[cconaf2]

Sorry it has been so long. I had to wait for some parts. I installed new Bosch plugs and it still runs rough. The old plugs smelled like gas as if the engine is running rich. Tomorrow I get my friends scanner and will do a diagnostic.