2000 4x4 3.4 Manual - Random misfire feeling

Hey all,

Looking for some help. Lets start by saying I have searched extensively for anyone with a similar issue to what I'm experiencing but have been left with no solid leads. I've owned my truck for over 2 years now and have been fairly meticulous with maintenance. (I'm a mechanic and car dealer by trade) About a month to 6 weeks ago I started to notice what felt like a random misfire while driving, usually in 3rd gear around 35mph or so. I started by replacing plugs, the fuel filter, then wires and coil packs. The problem has yet to subside and has seemingly gotten worse. Doesn't matter where operating temp is, doesn't matter what the outdoor temperature is, I've gone through several tanks of gas, etc. No cel the whole time. I've scanned for any pending codes and what not several times. For reference, the truck has about 280k or so. I have cleaned the maf, cleaned the throttle body, tested for vacuum leaks, and changed the air filter. I have an IAC valve on order, I cleaned mine but it seems to be original so I figured why not. Honestly I just with the truck would throw a damn code lol.

From here my head goes to possibly fuel pressure regulator but I'm fairly sure they fail at full pressure? Could make sense since it seems to happen most under very low load (basically just cruising, if I stay in it, it happens less.) When this started it would happen a couple times a day max but lately its several times every drive. Other thoughts could be a fuel pump randomly cutting out but usually fuel pumps work or don't. Maybe a sticky injector? Any help or brainstorming would be much appreciated!

Thanks in advance.

 

I have had those symptoms turn out to be a throttle position sensor.

 

I did replace the TPS shortly after getting the truck, it was an oreillys part as I was in a pinch so I'd be a bit disappointed if its failed but not surprised haha maybe I'll toss one of those at it tomorrow hah.

 

FPR's can cause this. These trucks are a pain to test the pressure, so it might be part of the parts cannon. I've seen 1 fail on a 3.4 in 15 years.

I'd be looking at fuel pressure, and likely checking the valves with a borescope for carbon, burn, or chips.

Another failing point is the igniter. Hard to test if its intermittent though.