Hello all, long time reader, first time poster. I've got a 1994 F-150 XLT with the 302 Windsor 2x4 single cab long box with just under 210,000 miles on her, all stock. I have recently replaced the rear 18.2 gallon tank, and the fuel pump and sending unit, as well as the 19 gallon side tank and its fuel pump and sending unit. I also replaced the fluid in the rear diff while I had the box off. I also replaced the fuel filter, fuel pressure regulator, and the IAC valve. All that said, she starts up just fine, but after warming up, she will often bog down when idling, almost die, then surge the throttle on its own, back to regular idle. It might do that twice if I let it, on the third time it will totally die. Starts right back up every time.
When driving, for the first 30% of the throttle pedal's travel, i will hear popping backfiring noises coming from what sounds like somewhere around the intake/air filter. If you keep pushing through that, the throttle will surge and then the truck will accelerate as normal.

I suspect that I've got an issue with the EGR valve, as the only vacuum leaks I have been able to find are around the EGR Valve itself (spraying brake cleaner method.)

I have not yet checked the fuel pressure at the fuel rails as I have already replaced nearly all of the fuel system up to that point.

Where should I look next? Thanks in advance!

 

I would start by inspecting and fixing the leak around the EGR valve. That alone could possibly fix it. You could cut a piece of a Coke can and place it between the EGR and intake. If that fixes things, you have a faulty EGR. If it’s sucking in the brake cleaner at the EGR valve, the vacuum hose has a leak there, evp gasket bad (not sure if that would introduce anything into intake) or the gasket blown out somewhere.

 

Thanks for the tip! I planned on replacing the egr valve next; knowing my luck i've got a bad egr valve position sensor and solenoid as well. I like the coke can tip!

 

If you do just replace the EGR, I would have the tube on hand also. Factory has a flex section, mine snapped there. Testing those parts is pretty simple and free before you replace them.

have you checked for codes?

 

Backfiring or popping through the intake is low fuel pressure or fouled inoperative injectors
I would check the fuel pressure pronto
I would also check the flow rate of the injectors
Get the EGR sorted out
Be careful with the tube
They break if you breathe on them wrong

 

I was already leaning towards picking up a new egr tube as well, but based on the responses thusfar, definitely replacing the tube. After further inspection/investigation, I'm 95% sure the existing egr valve, egr position sensor and solenoid are all the original "from the factory" units. "Mozzle" go ahead and replace it all while I'm at it.

I was afraid someone would mention the injectors. They sound expensive and with my luck, if there's an issue with one or more of them, cleaning/rebuild won't cut the mustard.

Again, I appreciate all the input!

 

Injectors are cheap at the junkyard if you need 1 or 2
You can monitor the fuel pressure yourself and at the same time manually fire each injector
I use a momentary contact switch like a hood release switch
That way I can cycle the injector and watch the pressure drop
Do that to each one and you might bne able to determine if any are bad
I ale have a test bench for injectors where I can run Ford injector flush through them and check the spray pattern
For now, you should just listen for the click and watch the pressure drop
Any that do not drop fuel pressure need to be replaced