Bad idle and poor fuel mileage

[Canadian]

Idle is very rough.
Motor has stalled going around corners sometimes.
Codes said O2 sensors so I replaced them.
At first, I thought great, the idle sounded better and smoother.
On the way home, flashing engine light again, and idle went back to being bad.
When I find the time I'm guessing injectors and or plugs.
I forget the code numbers, but will post next time I scan.

I have had a miss fire code from day one (intake gasket I think it was) but it only makes the engine light come on if I set the cruise above 130kmh for any length of time.
Truck still went like a scalded ape and mileage/idle was fine at that point.
Truck still works fine at high speed now, but mileage is down about 35%.

I'm fine with taking things apart and putting them back together.
Diagnosing I have trouble with.....

 

[Bonecollector]

Check plugs, coils and wires, sounds like ignition


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[gmac53]

our nbs 5.3 are notorious for the knock sensors. they are under the intake manifold and it would be best to get the harness as well. i just did mine and my truck ran 1000x bettter but back to rough idle and bad mileage. i havent read code yet but after relpacing i had advance auto clear code and codes at that time were for bad tps, i assumed it was from my egr not proprely seated but after sealing it i still have an intermitting rough idle. but even if its not the knock code it would be better to go ahead and knock it out itwill be a great investment i also replaced the injector o rings top and bottom since i was right there, dont forget the egr like i did lol


heres the link for the cheapest set of everything minus the new intake gaskets,


https://www.google.com/aclk?sa=l&ai...y=2001&utm_campaign=gb_csv_br&utm_content=EEK

 

[gmac53]

btw a good way to test sensor is tap or "knock" above or near sensors while at idle if idle changes sensors are goo. if motor fails to compensate for false knock then replace,