Truck stays running after diconnecting the IAC valve.

[ConnieGallas]

Do I know this is a vacuum leak somewhere. I'm fairly confident it's leaky around the throttle plate because I just took the upper manifold off and thouroghly cleaned it and all the related components, including the throttle body. I learned from s different thread that the throttle plate has a special coating applied by the manufacturer that seals the edges of the throttle plate. My question is, can I purchase this coating and apply it myself?

 

[RonD]

If engine was warmed up and you unplugged the 2 wires on IAC valve engine can stay running, but at lower RPM than with IAC valve plugged in

1996 4.0l might idle at 750rpm warmed up in Park, 800rpm in gear
Unplugged IAC should drop to 600-650 in Park

If unplugging IAC valve does not cause a drop in warm engine idle then you may have an air leak, not a big one
OR
Some one may have messed with the Anti-diesel screw on the throttle linkage, there is a screw that looks very much like an "idle screw" on the throttle linkage, but everyone knows fuel injected engines can't use an idle screw, so its called an anti-diesel screw, lol
But everyone should also know a fuel injected engine can't "diesel"(run on) like an older carb engine could do, so silly name for it
In any case if some one messed with it it may be holding throttle plate open too far


Not sure on a coating that would be for air leaks, the throttle plate rod leaks air, all do and all will, but not enough to cause an issue, if the rod is sloppy then replace the bushings or throttle body
Only other openings are sealed with gaskets

 

[cbxer55]

On mine it holds the idle higher than normal if I screw around with it. I've done so many times in the past. Wanted the idle higher, turned that screw, and Voila, idles higher. If you turn it too much, you will get codes for it though. There's a very fine line to be dealt with when adjusting that screw. Generally, I just make sure I can slide a piece of paper in there when idling and it's all good. Sometimes, I want the idle higher, and that screw performs flawlessly in doing so.

Must just be me and my old-fashioned ways of doing things. Or my 98 Ranger is just a pig-in-the-poke.

 

[Dirtman]

That screw is not there for you to be screwing around with it!

 

[gw33gp]

I adjusted that screw on my 89 STX to keep the throttle plate from sticking. I don't know why, but after about 8 years of owning it, the throttle plate started sticking a little when the engine was cold. I studied everything around the throttle body and decided to try adjust the screw a little. It solved the problem and did not change the idle. I never had a problem with it again.