I have a 4wd f-150 w/ 302 FI , 1991. Started and ran great til yesterday. I accidently left the key on and ran the battery down to zero. Replaced the battery, and now, theres no cold start help, and it idles a bit lower. By cold start help, I mean the rpm's do not increase when started cold, as a choke would do, and when I get it to idle after it warms up a bit, it idles a bit lower than it did. Need some advice on this qick, as I am driving 500 miles in it today. Vacuum? Fuse? Fusable link? Somthing with the TBI is wrong since I left the key on. Please help, thanks.

 

Does it still drive good when cold? I could be wrong but I would guess that when the battery went dead your KAM (keep alive memory) was erased, causing your truck to start from scratch. If it still drives normal I wouldn't worry about it. You probably just erased the PCMs memory of how the truck drives and it needs to relearn.

 

That is how my truck acts after I have disconnected the battery to reset the ECU. The computer has to "relearn" your driving habits over the next X number of cold starts. After I drive mine for 5 miles or so it starts to figure things out and all is OK. If you have time before your trip go for a short drive and see if it starts to run better. Hope this helps...

 

X2. This is correct and is what I'd do.

 

The cold start "Fast idle" it wouldn't be effected by loss of memory, function of coolant temp and tps information not driving habit.

Might simply be a bad/stuck IAB valve, rap on it couple times with screw driver handle see if it regains normal function.

If known to be "good", testing shows its free and will function if everything else is as it should be?

Test for power to it, should have battery voltage "key on" at red wire at the IAB valve, if not trace back check that circuit for trouble.

If tests 12v key "on" at red wire then use any suitable length of wire as test jumper, provide ground to White/light blue side of IAB valve, does idle pick up when good ground is provided?

If so you have a issue in that circuit, the "Wht-LT Blu" wire running between the PCM and IAB valve. Test that circuit for continuity, test its run between PCM and IAB valve connectors, if result is zero trace back locate problem or simply run new wire.

Might be other issues but that should give ya little something to start with narrow down any minor issue it might have.

 

Have re-started it about 8 times, driven it about 12 miles since, and no change. Also noticed a foul sulpher like smell since this happened. Thought it might be my temporary fix of the ehaust manifold with goop weld, just burning off, now im thinking it could be a sensor type problem. I will try wrapping on the IAC solenoid and check wires.