First, hello.

2003 Ranger 4x2 , 2.9 V6 with auto trans, Edge with just under 262,000 miles. I've had my local mechanic look at this but they were not able to fix it or find the problem. I'll explain in detail.

When it's warm out I start the truck in the mornings to go to work, choke seems to race the engine longer then I feel it's needed. Once it dies down to normal, I drive off.
When I turn on the A/C at idle, it run as normal as I guess it use too, slight drain on engine and it cools very well. While driving however, when I need to slow down or stop, the engine seems locked at a fast idle and races over 2,000 RPM's. What I have to do, is turn OFF the A/C, and in an instant, engine idles down to normal.

I can be costing and the engine will idle over 2,000 and will be traveling at 40 to 50 mph with foot OFF the throttle, for 1 to 2 miles. IF I turn OFF the A/C, it idles back down. I'll drive and shift into neutral with foot off peddle, and watch the tach reach 2500 to 3000 RPM's

This ONLY happens when the A/C or the defrost in winter is running. I am at a total loss as to why and seems my mechanic, who we've used for 20 years and has been fantastic, can't figure it out either. He has re-programmed the computer with no effect. The A/C pumps out cold air just fine.

Open for questions.. please any ideas at all??
Thank you!

 

Welcome to the forum

Mechanic didn't check/clean or replace IAC Valve?
Even if he's only been around 20 years he should know about IAC Valves

IAC(idle air control) valve is what the computer uses to set idle RPMs, on ALL fuel injected engines, not a Ford thing
IAC Valve controls an air passage the by-passes the throttle plate

When engine is cold computer does run in Choke Mode, so sets a higher idle using the IAC Valve, opens it more, then closes it bit by bit as coolant/engine warms up

When you shift into gear(automatic) computer should bump up the idle a bit, using IAC valve
When you turn on the AC computer should bump up the idle a bit using IAC Valve

So it all comes back to........................IAC Valve

It can be removed and cleaned or replaced, but FIRST you need to check for a Vacuum Leak

Locate IAC Valve on your engine, have a look here: http://bob-ayers.smugmug.com/photos/124318500-L.jpg

After engine is warmed up let it idle, unplug the 2 wire connector from the IAC Valve, it should close and idle RPMs should drop
RPMs should go down to 500, engine barely running or engine may even stall, either is GOOD no vacuum leaks

If RPMs don't drop right away but slowly drop then IAC Valve is sticking, needs to be cleaned

If they don't drop at all you have a vacuum leak, may PCV Valve, these should be changed every 3 oil changes


Cleaning IAC Valve seen here: https://www.ranger-forums.com/how-di...-valve-142103/

4.0l engine but cleaning is cleaning

 

RonD. Thank you for the reply. I'm sorry I forgot to mention that this IAC valve was replaced by another repair shop. My goto shop cleaned it, and reset some computer info.

I unpluged the wires, and idle dropped some RPMs but no where close to stalling. I plugged it back in and engine raced then settled down. AC was OFF. To be honest, I don't recall why the first IAC was changed out. I'll replace the PVC valve tomorrow anyways. Is there a gasket on the IAC valve that I need to replace if I should take it off and clean it further?

Thanks!

 

Yes, there would be a gasket but it reads like IAC Valve is working, RPMs did drop when unplugged and did go up when plugged back in, so no reason to pull it off yet
BUT...............RPMs didn't drop far enough

Do same test after new PCV Valve is installed

If RPMs do not drop to 500, you can then check the "anti-diesel" screw on throttle linkage and also the throttle plate itself
On the throttle linkage is a screw that "looks like" an idle screw, but everyone KNOWS that fuel injection can NOT use an idle screw because it has no Jets, so computer needs to set idle so it can meter fuel flow

Find that screw
Warmed up engine, let it idle
Unplug IAC Valve, RPMs should drop
Turn screw counter-clockwise(unscrew) 1/2 turn and see if RPMs drop more, if so turn it 1/2 turn more, repeat until engine is almost stalling, someone was messing with this screw without knowing what it was
If 1/2 turn does NOT cause drop in RPMs then turn it 1/2 turn back to were it was, and leave it alone

Check throttle plate
Move linkage a bit to see if RPMs change, could be an air leak around the throttle plate shaft
Also check that the spring on the throttle feels tight, this spring has to "snap closed" against 30+ inches of vacuum when engine is decelerating.
Also check that gas pedal cable is not sticking

As far as you know has the TPS(throttle position sensor) ever been changed or worked on?
These can be installed incorrectly and they will hold throttle plate open a bit, won't let it close all the way