2004 Ranger Edge 3.0L Manual 2wd

Upon start up, with accessories off, the truck runs at 2,000 RPM and slowly creeps up to 3,000-3,500 RPM without touching the throttle.

If you drive it right away it will keep pulling in gear until you push the clutch in, then the idle will return to 2-3,500 RPM at a stop sign/light

After about 5-10 min of either idle or driving, the idle cuts, the engine ALMOST dies but then returns to a normal idle of 5-700 RPM.

No Codes

Ive already replaced:
IAC Valve
TPS
MAF sensor

Cleaned the throttle body (no i didn't remove the "coating")
Checked for vaccume leaks
Inspected throttle cable/butterfly closure


Thoughts? Feelings?

 

Welcome to the forum

First lets see if the problem is an air leak or the computer/wiring
Warm up the engine to operating temp
Let it idle
Unplug the two wire connector on IAC Valve
IAC Valve will close all the way
RPMs should drop to about 500, or engine may even stall, either is OK, it means no vacuum leaks

If idle stays high, 700 or higher, then there is a leak, or "new" IAC Valve is not closing all the way

If idle drops down then computer or IAC valve wiring is causing the high idle

The computer sets Cold engine idle based on ECT(engine coolant temp) sensor, normally Cold engine will idle at 1,100-1,300 unless it is VERY COLD
ECT sensor is not expensive, so I would just replace it on spec
There are TWO temp devices on the engine
ECT sensor will have Light green wire and a Grey wire, only computer uses this one
ECT Sender is ONLY used by the dash board temp gauge, usually has just one Red wire

You of course want to change the ECT Sensor, not the sender


You may want to call or stop by a Ford dealer and give them your VIN
Have them look it up and see if there is a software update for your computer, that dealt with high idle issues, there were some "glitches" in the early 2000's than needed to be patched with new software.
If won't be free, but would need to be done
Because there are no codes set I would lean towards computer problem, but when you unplug the IAC valve while engine is running you should get a CEL for IAC valve circuit failure, if not then that would also indicate computer has a problem.
Unplug MAF sensor while engine is running and you should also get CEL and MAF circuit code

IAC valve will get 12volts(battery voltage) when key is turned on, IAC Valves GROUND wire comes from the computer and this is how the computer controls the IAC Valves position.
With key ON, computer starts up and Grounds the IAC Valve to fully open it for starting
After startup the computer starts to Pulse the Ground to close IAC valve to set "target" RPM

If IAC Valves ground wire to computer is shorted to a ground(metal) then computer can't close it, or if computer is damaged it can't close it.

Remove IAC Valve from intake and plug it's wires in
Turn on the key and valve should open all the way
Unplug the wires and it should close all the way
Plug them back in and it should open
Repeat a few times just to make sure the "new" valve is working OK

Unplug and Test the wires with volt meter set to DC volts, engine off
One should have 12volts with key on, remember that wire, should be RED
Other wire should be a Ground, with key on, White wire
Turn key off and see if it is still a ground

 

Upper plenum gasket under the intake manifold. NAPA #FPG MS94429. they're like 10 bucks. takes to 2 hours to do. I had similar symptoms. Found out there was a vacuum leak in this gasket. Replaced it and the truck idled like new. Apparently its common for this gasket to dry out every few years.

 

Thanks for all the help! i will try further evaluating the IAC valve with a voltmeter when i can get my hands on one (Friday) and let you guys know how it goes!

Im tempted to shy away from the plenum gasket being bad, a few years ago i had the valve seats go bad in my heads so i replaced all the gaskets when the heads went off to the shop. so in theory the gasket should be brand new. That being said I will keep it in mind if the IAC or computer isn't solving the problem!

 

Test for vacuum leak FIRST, most common issue, by unplugging IAC Valve while engine is at warm idle.

The thing about "new" in the last 20 years or so..............
"New" used to means tested and working

"New" now means "You test it and we warranty it"

Ford, and most automakers, still demand Quality Control on all supplied parts, also documentation that parts are not made in "sweat shops", lol.
This is why Ford Parts are more expensive that 3rd party parts, sometimes MUCH more expensive.
Quality Control means Labor, testing parts or a sample of parts after assembly takes man hours, and labor is expensive.

3rd party manufacturers don't do Quality Control, or R&D, they make the parts and send them out, with a warranty, buyers of the parts are the Quality Control Department, and free labor, in fact they pay to do it by buying the part the first time, lol.
And we want cheaper cost on parts so this system is of our own making, so you have to take a part back to exchange it, your labor is free, to the parts supplier.
If 3rd party maker gets too many "returns" then they look at the part to see where problem is, or discontinue it

If you think, or wonder why, Auto repair shops are expensive, yes it is higher labor cost but also Parts cost because they HAVE TO use OEM(Ford) parts.
They can't afford the cost in money, or reputation, to replace 3rd party installed parts under warranty, labor is way to expensive to do this for free.

 

Okay so,

I actually forgot to mention that i did replace the ECT sensor as well. It looks like there are two near the thermostat housing, one has black and red wires, one has grey and green. I replaced the one with grey and green. still no fix.

The IAC...
-Has good voltage coming from the connector(12.1v) but when i take it off and watch it, it doesn't close all the way / very little movement in the valve.

-Has good ground when key is off.

-When i unplug it while the engine is running, it used to stall immediately, now it runs at 4-500rpm with no codes.

My take away is that my computer is fried due to the absence of error codes when the IAC is un-plugged??

should i try PCV replacement? I've heard about CPS sensors possibly causing this issue as well?

 

IAC Valve unplugged on WARM engine and RPMs at 500 or stalling is the same thing, no vacuum leaks
has to be warmed up engine, cold engine will always stall

PCV system issue is a vacuum leak, so would how up on the test above.

Not sure how Cam position would change idle, CPS is used mainly for fuel injector timing, inject fuel when intake valve opens on each cylinder so less loss of fuel on the port and back of valve.
It also helps with spark timing, more fine tuned than Crank sensor

So yes, pop the top on the computer and have a look at circuit board, also the connector

ECT sensor has a Cone Shape tip
ECT sender has a Cylinder shape tip

Sensor image here: http://www.allfordmustangs.com/forum...ocated-ect.jpg

Sender image here: https://www.obd-codes.com/faq/images/ect-sensor.jpg