94 F150 High Idle

[AK_F250]

1994 F150 XLT 5.0 e4od ac low mile long block. Owner was told by someone that it needed an ecu, no idea what troubleshooting was done.

And that's about all I know about it. It idles high (no tach) in gear, drops to normalish after a second in neutral, and the throttle seems to hang for a second or two in park warm. Overall the idle seems sporadic . I gave the vacuum lines a once over and replaced a section of rotten collapsed line between the intake and valve jobbie going to the charcoal canister. No visual problems other than that. Ac on/off has no change. Up to temp with the iac unplugged it idles a little on the low side occasionally but overall much better, I'll start it up again cold and unplugged once it cools down. I haven't worked on one of these in 15 years, what should I be looking at or testing?

 

[TrikeKid]

I'd make double sure you've got no vacuum leaks, with the IAC unplugged it'll react like a carbed engine to spraying brake cleaner around. I had a bad plenum gasket cause me all sorts of issues on a mustang I used to have.

If that all checks out, set your idle with the IAC unplugged and the engine hot and verify the TPS reads .98-1v with the throttle closed.

 

[welndmn]

Buy a little smoke machine off amazon and chase the vacuum leaks.

 

[Gdogg]

What’s the fuel trims at? I’ll bet they are pegged.
Probably a vacuum leak, a smoke machine will help find the problem.

 

[AK_F250]

I found an iac in a box of old ford parts I forgot I had, threw that on and it was 95% better all around, still something up but I suspect the owner fucked with it and caused what's left of the idle issue. He replaced the engine because of the idle and had bought a breakout box but says he never used it and got really quiet when I told him I thought the problems that are still there were from someone adjusting shit randomly. Could very possibly still have a small leak somewhere too.

Good enough for now, it's a summer toy so I'll probably mess with it more next year, I saw some other things that need to be addressed anyway.