I am having a problem with cylinder 4 and 5 misfiring at idle when it is warmed up. It runs fine when its cold with no misfire I had a scanner hooked to it, no codes other then the misfire. I went into mode 6 in the data stream and found 4 and 5 misfiring. I have swapped the coil packs, injectors, plugs, and wires. I sprayed the intake gaskets down with brake clean n no leaks there. Fuel pressure is good. The misfire did not move. Then I did a compression and leakdown test. compression checked out good but checking cyl. 5 for a leakdown (it was on TDC on compression stroke) it built up pressure then shot out the exhaust. Did that a couple times, then it held and stayed (no leaks), then took the tester off rolled the motor over again, got it back on TDC on compression and it did the same thing. So then I was leading towards a valve guide being out. pulled the heads, got them apart and there pretty just normal wear on them. nothing out of the ordinary. Does anyone else have any advice for me??


2000 Silverado 1500 4wd 5.3