4.0 High Idle

[Shikai2070]

Have a 92 ranger with a 4.0l. Dealing with a high idle issue. Around 1500rpm. Tried cleaning the IAC and it didnt seem to help. Can verify it moves when 12v is applied to it. If I unplug the iac the idle drops down to 1000 rpm or so.

 

[Eddo Rogue]

I had a high idle issue, apparently its common on the 4.0, and could be many things. Mine turned out to be the throttle body. I taped the hole shut on the throttle plate and it dropped my idle nicely, so I filled it in with solder and drilled a smaller hole, idled and ran great until I was able to replace it.

Anyways if you want a quick test, you can try taping over the hole on the throttle plate and run it.

 

[Shikai2070]

I had a high idle issue, apparently its common on the 4.0, and could be many things. Mine turned out to be the throttle body. I taped the hole shut on the throttle plate and it dropped my idle nicely, so I filled it in with solder and drilled a smaller hole, idled and ran great until I was able to replace it.

Anyways if you want a quick test, you can try taping over the hole on the throttle plate and run it.

Will that cause issues? Shouldnt the hole be left open if its there by design?

 

[PetroleumJunkie412]

You have a vacuum leak.

Propane test or smoke machine.

 

[SenorNoob]

You have a vacuum leak.

Propane test or smoke machine.

THIS!^
1000RPM with the IAC is WAY too high. Your drawing more air somewhere.

 

[Eddo Rogue]

Will that cause issues? Shouldnt the hole be left open if its there by design?

Well on mine I think the gap between the plate was compromised. making more air than usual pass thru when closed.
This was a diagnosis/temporary fix. I did replace it with a new one.