Hi everybody, I'm glad this site exists and I hope you all can lend me some insight into my problem.
I rebuilt the head on my 98 tahoe after a blown head gasket and replaced the fuel pump and fuel injectors (with the new MFI setup) on it. The car runs but has a rough idle, poor fuel economy, and throws a p0300 DTC (random misfire). Looking up the fuel trims, bank 2 is pretty much maxed out (25% LTFT 14%STFT) and bank 1 is at 10%LTFT. I've tested the fuel pressure, which seems to be fine, as well as the manifold pressure, which pulls a healthy 19 in Hg vacuum. The rough idle exsists both immediatly after startup when the fuel system is in open-loop mode and after warm up when it is closed-loop, so I don't think its an O2 sensor issue. The egr valve seems OK.
Even though its pulling 19inHg vacuum, is it still possible a vacuum leak could be causing this? I've tried checking for leaks with wd-40, propane, etc. but no change in the idle.
Could an exhaust leak do this? How large would it have to be? I replaced a busted check valve on the air system but that seemed to have no effect. There aren't any obvious sounds of an exhaust leak.
Is it likely the new fuel injectors I installed are bad? Maybe they're plugged with debris?
I'm just running out of ideas. All I know is that everything I check seems to be OK. I will be eternally grateful if anyone can help me figure this out.