99 ranger high idle

[99MOranger]

hi, i'm new on here, and my ranger has been giving me some trouble so i thought id try this. First off its a 99 XLT 5-speed 4x4 3.0L

Whenever i go to start my truck cold it starts at 2,000 rpms, and goes to 1100 quickly, but after it warms up and the engine gets hot it idles at about 900 rpms. If i'm driving it around for a while it and come to a stop and push in the clutch it idles at 1100-1200 rpms for maybe 30 secs. and then settles down to 900.

I'm starting to get very irritated at this because I've replaced the IAC, EGR valve(had a vacuum leak, did a smoke test and that was the only spot), throttle position sensor, cleaned the throttle body. Also I've reset the computer multiple times throughout all this. one last thing is that the curb idle screw is backed out all the way, this was apparently done by the previous owner.

I just don't know what else i should do, any suggestions?
Thank you for any help you can give me.

 

[Froggmann]

The symptoms you're describing are absolutely normal. It's normal for an engine to rev when cold and it's normal for these trucks to hang at a high idle at a stop light for a few seconds. Ford designed them to do that, only way you could cure it is reflash the ECU.

 

[griz700rocket]

http://www.explorerforum.com/forums/showthread.php?t=79362

You might look into this.

 

[RonD]

Yes ^^

When starting a fuel injected engine the computer opens the IAC(idle air control) Valve all the way, so you usually get startup RPMs above 1,800 and then computer closes IAC valve to get to "target" RPM for engine temp.
Cold engine idle is usually around 1,100rpms, it is engine temperature based, colder is higher, warmer lower

But your warm engine idle(900) is a bit high IMO
Manual trans should be 650-700, automatics are higher, 750-800rpms usually

After engine is warmed up unplug IAC valve, it should close and idle should drop to 500rpms or engine may even stall.
If it doesn't drop then PO may have adjusted the anti-diesel screw and it is holding the throttle plate open, it isn't an "idle screw" even though it looks like one.
Back out the screw so idle is lower than 600rpms, this will allow computer to reach its "target idle" of 650 using the IAC valve.
Unhook battery for 5 minutes, this will cause computer to reboot on next startup and relearn IAC Valve settings, this can take a few drive cycles.
If screw is not holding throttle plate open and idle is still high(900) try manually closing the throttle plate more(see below), if that doesn't lower idle then you have a vacuum leak somewhere, not a big one, but there is one.

To reduce emissions the computer will hold idle higher for a few seconds when clutch is in and speedo is above 5MPH, 30 seconds is too long.
Check throttle cable and cruise cable for binding, also check throttle plate spring, it needs to be strong enough to pull throttle plate closed against the engines pumping of air out the exhaust.

 

[Froggmann]

My 99' idles about 8-900 rpm when warm. When adjusting the TPS make sure you don't go over .90v, it may make the high idle issue worse. When I did the composite intake swap on my truck, it would rev between gears and idle at 1500rpm. Found out the TPS voltage was .95volts, lowered it to .88v and it cured the problem.

 

[99MOranger]

well the screw is backed out all the way, so its not even holding the throttle plate open. how do you adjust the tps sensor?

 

[99MOranger]

and Froggmann how did you adjust the tps sensor? or did you do it the way the article says too? because your symptoms are exactly like mine.

 

[RonD]

I would check the throttle body for build up holding the throttle plate open.
TPS bolt holes are slightly elongated allowing adjustment(rotation) if loosened.

But make sure throttle plate is completely closed and engine RPMs warm can be brought down to at least 500RPMs with IAC Valve unplugged.
If you can't get warm engine idle down to 500RPMs then TPS adjustment won't help.

 

[Froggmann]

I would check the throttle body for build up holding the throttle plate open.
TPS bolt holes are slightly elongated allowing adjustment(rotation) if loosened.

But make sure throttle plate is completely closed and engine RPMs warm can be brought down to at least 500RPMs with IAC Valve unplugged.
If you can't get warm engine idle down to 500RPMs then TPS adjustment won't help.

X2

I had to slightly tweak the throttle stop on the TB shaft to allow enough adjustment in the TPS holes. If you make any changes to the throttle shaft position, be sure to check/adjust TPS voltage.