P0300 code still!

Hey everyone, I got a P0300 code (random/multiple misfire) today. Lately my truck has been feeling a little under power whenever driving it. And when I cold start the truck, the truck will have a rough idle and shake for 10-20 seconds. And after that, it will idle normally and sound fine. The truck also jerks when I drive up hills. The spark plugs, coil packs, fuel filter, and injectors were changed around 20,000 miles ago. Truck is the 3.4L v6. Does anyone have an idea what could be causing this code? I have a feeling it could be a O2 sensor Any help is appreciated! Thanks!

 

Check your coolant level. You could have a head gasket leak like I did. Same symptoms.

 

Always start with new plugs

 

Assuming that no issues 20k ago after plugs/coils/FF/injectors installed……
U can rule out bullet points 2-8
Rule out ECM too

as u state, once lil warm runs OK
Intake leak?
Metal/rubber expands once heated up then no leaks….appears to run fine
Test: spray carb cleaner on air intake and intake manifold while engine running
If Engine changes RPM’s….there is your leak

-clean MAF sensor with SPECIFIC cleaner
-bench test or just replace coolant sensor
-test F pressure…..if not 39-45lbs….replace fuel pressure regulator (cheap) if no change, replace FP in tank

HG issue could cause misfire, but if no overheating/no low coolant unlikely
Test: pull your newish plugs, if rusty from water/coolant, very possible HG
GL

 

The P0300 code is telling you that you have a problem that effects ALL cylinders and is not individual cylinder specific. Start with a compression test. If it was me I would start it cold and let it run for maybe 3 seconds then pull the plugs and look, if a plug or plugs are saturated, then sniff and touch the plugs to my tongue. You can taste smaller amounts of coolant than you can smell.