1998 4.0L auto Ford Ranger irregular idle

[Wicked_Sludge]

i wouldnt start replacing parts untill we identify the problem.

for the IAC, its best if you can soak it for a little while...but spraying it down is better then nothing. ive also heard that a drop of oil on the shaft of the valve can help.

 

[warhawk]

The 4.0L are notorious for having a ticking noise come from the valve train. They don't get as oiled as well as they should. I'd check the motor with a mechanics stethoscope or a screw driver but if it sounds like its coming from the valve covers it's a good chance its the normal 4.0L tick.

 

[rickcdewitt]

4.0l IAC

i have a 94 exploder that was doing the same thing so i looked into it and found in alldata that the IAC can cause that wah-uuh-wah-uuh. the rpms rose and dropped very evenly in amount and duration. i pulled the IAC cleaned it as best i could.i didnt see enough soot to make it jam but it did make a difference.i had to drive it for a while before it quite surging 100% of the time.if you decide to just throw parts at it i would go for the new IAC.ive not heard that the tps sensor could do this also as it doesnt regulate the idle though it does have input on spark and fuel.

 

[Wicked_Sludge]

adjusting spark advance and injector pulse width is more than enough to cause a +/-200 change in RPM. it wouldnt be the first time a faulty TPS has caused "seeking" idle.

 

[94 splash]

well with the hi/low idle i would just check all of the vacuums caps... just to make sure b/c i had the same prob with my old 2.9 and it come to find out that the one cap split and you couldent even tell it was until you took it all the way off.. But would also consider an intake

 

[opbeagler1]

i had the same problem on my 96 super 4.0 , it turned out to be the egr valve was rusted out on the underside of it,where you coundnt see it. causing air leak.

 

[koocuz]

SOLVED!! At least for now

Sorry it has taken so long to get back to you guys but you wont beleive what was wrong with this truck!! Apparently at the dealer when it was new they installed the AC in the truck. Its not really aftermarket, its a ford AC kit that looks just like the factory kit. Well, the kit has its own fuse and relay (in a wire harness) some joker decided to put the factory fuse and relay (in the fuse box) it somehow glitched with the aftermarket system and caused it to idle low/high. I pulled out the factory fust and relay and it runs perfect!! And the ac works just fine. This is the craziest thing ever but its fixed now.

I will check on the mounts & ticking later..