1993 F-150 w/302 EFI stalling, surging?

[MadJimbo]

Wife's 93 F-150 with 302 EFI engine starts and immediately stalls, unless you keep reving it up. If you can keep it running, it stumbles and surges almost constantly!

It has been getting slowly worse for last couple months, up to the point now, as stated above. Over that time I've changed the plugs, wires, pvc valve, fuel filter, checked for vacuumn leaks and even changed the oxygen sensor, all with temporary "slight", or no improvement! I've seen other links suggesting the IAC valve. Think that's the the problem?

Need some expert help (for the truck too ), as I'm an old school guy who'd rather be tuning a caburator! Can anyone help?

[unclebubbles]

It could be the iac, but normally you would be able to rev it and keep it going. Do you have two tanks, can you switch to the other tank if you do and see if it does the same? Either rig up a gauge, or take it somewhere and have the fuel pressure checked. You cant rely on just checking to see if its pumping fuel at the valve on the fuel rail. A drop in pressure of as little as 5# from a pump getting weak can cause problems.

[MadJimbo]

Thanks for your suggestion! Yes, it does have two tanks. I switched to the other and it does the same thing. Got to keep pumping the gas pedal to keep it running. Just reving it up to say, 2000 rpm and holding it there, it will still lose rpm and stall after a second or two! Maybe after warming it up with the constant reving for about five minutes, it will stay running and has good normal acceleration when you step on it, but once you level off to a constant rpm or drop to idle at a stoplight or something, it'll start it's bucking bronco routine and may stall if you don't kick into neutral to rev it again!
Just hoping not to throw more uneccessary money at it!!

[unclebubbles]

Ok, double check your vacumn lines and look for leaks, especially the one that hooks to the pcv, and most especially the one going to the map sensor. Also check the map sensor itself, the symptoms you mentioned in post#3 makes me believe that could be your problem, the fact that it smooths out and takes off when you give it more throttle.

[MadJimbo]

Changed out a couple vacuum hoses that were a bit weathered which only made a very slight improvement. Then changed out the MAP sensor, and that was the ticket!! Thanks!

[unclebubbles]

Glad you got it going, thanks for letting us know.