Idle spec for a 94 4.0 ?

[Andy D]

The Rat idles at ~12 or 1300 rpm until it has been running for a 1/2 hour. Even then, it idles at just under 1000 rpm. Is this normal? I have no clue , my last Ford was a '75 Country Squire. The idle is smooth and there is no hesitation when taking off. Its a minor issue and if the remedy is too much trouble, I'll just add it to the to do list. Are there things I should check? TIA

 

[adsm08]

Sounds a little high, not too much. It should be around 750 or 800, maybe 850 if you have an auto.

Probably a bad temp reading or a sticky IAC. I would not worry too much. Put it on the to-do list and worry about bigger problems. Mine used to idle at 2000. That was something to worry about.

 

[RonD]

My '94 4.0l idles cold at 1,000 then over 5 to 10 minutes as it warms up idle will slowly go down to 700, manual trans

After engine has warmed up, depending on outside temp that should be no more than 10 minutes, if longer T-stat may have a problem, not closing all the way.

After engine is warmed up unplug IAC valve while engine is idling, idle should drop to about 500-600rpms.
If it does it means computer was holding idle high for some reason, could be ECT sensor, but that will usually turn on the CEL after 10-15 minutes.
If idle doesn't drop then plug IAC back in and shut off engine.
Remove throttle/cruise cable from throttle plate linkage.

Repeat above, start engine unplug IAC valve, if idle drops to 500-600 then one of the cables is holding throttle plate open, maybe a bad throttle cable Mod?
Or cruise control vacuum switch is leaking causing a slight pull on the cable.

If idle is still high look on the throttle linkage for the set screw, someone may have turned it in too much thinking it is an "idle" screw like on a carb.
It isn't, it can set a "base idle" at 500-600rpms to prevent engine stalling if IAC fails and it can also be used to fine tune TPS "idle" voltage, but that is usually not an issue since later model computers learn TPS voltage ranges.

If idle still stays high then there is an air leak somewhere.

 

[Andy D]

Apologies, it is a manual transmission. no cruise, no AC. A sticky cable or throttle body linkage is worth checking into. I was engaged in replacing the R R parking brake cable when the weather closed in. The original was rusted solid. The Rat sat for a year under a maple tree in a backyard before I rescued it. Going into its third yr of ownership, it is probably time to take a peak under the hood. I have been trying to avoid it. I dont like the way this truck crumbles when I touch it. Please dont take this as Ford bashing. The truck was nearly rusted solid in places. Other places, it is just missing.
Would weeping valve covers create a vacuum leak ? The idle is high, but it is a good idle. it doesn't surge. Thank you for your advice.