I have a 2000 tahoe z71 5.7L v8 vortec 4wd TBI. I originally got fault codes p0300 and p0304. Since some part replacements i am currently getting p0300 only. My current vehicle symptoms are low MPG, seems starved for air, backfiring on acceleration only, reduced power, slow on acceleration. The parts i have replaced are plugs, plug wires, distributor cap and button, fuel filter, sea foam added, cleaned throttle body, and verified EGR valve is functioning. I have suspicion of faulty PCV valve. I tried to check for intake manifold leaks with carb. cleaner but uncessiful if there are any. Any advice or information would be greatly appreciated..

 

Ive experienced and issue where my 1997 gmc would have a hard time starting and once it would start it would sit and backfire and run like garbage.. I tried new rotor and cap along with new wires and plugs.. this did not fix my problem the root of my problem winded up being my fuel pressure regulator located underneath the plastic upper intake.. after doing so I no longer had the issue and it ran like a top again..

 

My '99 Yukon 5.7 had the crappy plastic base distributor that caused misfires on acceleration Had to replace it at 80k miles.