I suspect I have a bad or dirty injector. Noticed mostly at idle (running rough with knock sound)and lugging up a slight grade even at low highway speeds. Keep getting code for "Misfire Cyl 8" even after new IAC, coil, plugs, wires, and two sets of cap and rotor. Oh, and this all happened just after my plenum upgrade.

I can pull the boot off #8 plug and hear spark. I'll be checking the compression hopefully tomorrow if I can borrow a gauge, but I really think it may be fuel related, or anyways I hope it is not a cracked head or valve/lifter problem

Anyone with suggestions???? Thanks in advance!!!