Hi, this is my first post and hope someone can help me. I have a 2003 Ford Ranger Manual 3.0L. It is doing some weird stuff. 85% of the time everything works as expected, When it idles down to 700 RPM at a stop it never revs up or stumbles. When you start the truck it does the normal rev up and then settle down to idle as per normal.

Symptoms:
- Intermittently while coasting with clutch still engaged it will slow down to say 1200-1400rpm and then keep going for a random amount of time. Most times you let off the gas it will go down to about 700 rpm.
- Intermittently if you are at about 1000RPM when you let off the gas, it will actually speed up to about 1200-2000 rpm for random amount of time.
- When it quits doing this the feels almost as if the throttle plate was stuck open a bit and slammed shut. The change from maintaining or increasing speed stops abruptly and harshly.

Attempted Repairs (disconnected battery for 30-60 minutes after each step to relearn):
- Scanned for any codes, none found.
- Replaced IAC Valve
- Replaced TPS
- Cleaned MAF Sensor with proper cleaner
- Sprayed entire engine with carb cleaner to detect leaks. Found nothing that changed RPM
- Replaced PCV Valve
- Oiled throttle cable and ensured smooth resistance free operation
- Put a stronger return spring on throttle
- Checked TPS with scanner (%) and Multi-meter(V) and found no inconsistency. The graphs all show a smooth transition from closed to open throttle. Closed is under 0.9V
- Checked for voltage and ground at the IAC which checked out fine
- Removed and thoroughly cleaned throttle body. Inspected throttle body for damage around throttle plate and that the plate could close fully
- Replaced the IAC twice more since everything i can find online says IAC and i thought maybe bad batch or brand.
- Unhooked the battery a couple more times to see if it wasn't relearning idle properly
- Sprayed a liberal amount of Seafoam Upper Cylinder Cleaner into the throttle body while keeping it rev'd to burn it off
- Ran Prolab Injection Cleaner through at a strong does for over 4 full tanks of fuel
- Vehicle would idle at 650 RPM without IAC plugged in so adjusted the throttle stop screw until the engine is a hair away from stalling without the IAC

Things of Note:
- When i checked the PCV, The weird pipe that runs down the inside of the runner of the intake has a decent amount of oil in there. It will drip a decent amount out if left pulled out
- This issue popped up out of nowhere about a month ago
- When you unplug the IAC the engine does almost or completely stall and when you plug it back in, it does rev up and then settle back to idle telling me its at least working to that basic standard
- When i removed and cleaned the throttle body, I filed the holes on the TPS to reduce it a few % (I had an issue like this on my 2000 mustang where for some reason it needed to see a lower than normal signal to sort out idle), adjusted the throttle stop screw and disconnected the battery for 45 mins, it seemed to completely correct the issue for about 3 days. It then gradually started again holding or accelerating the vehicle for longer periods of time till it was basically right back the way it was when i started.

Thoughts:
- From what I can find online the IAC should be closed when unplugged but all 3 of the ones i have are fully open. Don't know if the ones for these vehicles are supposed to be.



- Thought maybe even though there is 12v at the plug maybe it was stuck at 12v and leaving the IAC open or something. Tried unbolting from intake. Plugging the ports enough so the engine almost stalls out to see if the plunger would actually move. If i let it rev up by manually letting more air in, if i restricted all the air till it stalled and even if i moved the throttle, the valve never budged. I don't know if this is normal because my test idea was flawed.

Any help would be greatly appreciated. I spent 2 days searching online and i can't find an issue quite like mine and any issues that are close to mine have resolutions i have already tried.

 

Welcome to the forum

Couple of things
TPS just reports throttle plate position, so doesn't control anything, its primary purpose is to give instant throttle response when driver "steps on the gas", as the MAF sensor is too slow, so engine would stumble without TPS, its also used to shut off injectors when coasting, foot off the gas pedal, to save on fuel

Ford IAC Valve is a true Solenoid valve not stepper type, so should only be replaced with a Motorcraft or Hitachi brand IAC Valve, those are the only brands that have solenoid type, others are hybrid stepper type
IAC Valve gets 12v with key on, this red wire has same voltage as vehicle all the time
Its Ground wire is the control wire, from the computer, computer Pulses the ground wire to lower or raise the voltage to close and open the solenoid
With key on engine off you should see about 11volts, engine running at idle about 7volts, but doesn't really matter.............
There is no "set voltage" for IAC Valves, the computer "learns" IAC Valve voltage and adjusts it constantly based on RPM feedback, and its accurate +/-4rpm

Because this valve seems to be working as it should most of the time, then diagnostics would point to a "control" issue, the computer, read on
OR, its the wrong type of valve

Emissions
Engines are required to stay above 1,000rpms if vehicle is moving, if speedometer is above 5MPH lowest idle should be 1,000rpms
Under 1,000rpms means higher emissions, engines need a Richer mix at idle so they don't over heat and to keep the Cat converters HOT

Manual transmission models are required to hold RPMs high when shifting gears, so when clutch pedal is pushed down, when moving, RPMs should hold high for 5 to 7 seconds, then drop to 1,000rpms if pedal is held down longer

But shouldn't go up as described
It reads like all your equipment is working like it should, which brings it down to a computer issue

Ford may have a Software update for your VIN, there were issues in the early 2000's for what you describe
You can check with a local Ford Dealer to see if an update is available, have VIN ready, 2003 is 19 years old so they may no longer have it, usually Ford does 15 years old as the limit, but free to ask
Even if you can get original software re-loaded it might fix a glitch causing the issue

PCV Valve can be a Vacuum leak, and so can EGR valve but........................computer should set a "high RPM code", overspeed code if this is happening
The absence of overspeed or underspeed codes would seem to indicate the Computer is setting the higher RPMs so it sees no error and sets no codes

 

Thanks for the response. I just called the dealership and they have no TSBs for this type of issue for that year of Ranger even using the VIN. They gave me a general TSB 03-3-5 but said that nothing in there will likely help me resolve the issue. The dealer is telling me 2-3 weeks for a IAC from them since im in Canada and they have to transfer them from the US.

I wonder if there is a clutch switch issue? maybe the truck thinks the clutch is pressed when it actually isnt.

 

IAC valves rarely fail but are often replaced, lol
Just go to local wrecking yard and get an IAC valve, same valve was used on multiple Ford engine models, you have pictures to ID correct fit

Whats bugging me is NO Codes
Try this
Unplug the MAF sensor and start engine, if its starts
Should get CEL(check engine light) to come on and stay on
Sanity test for computer
Plug MAF back in and CEL should go off, any codes set will self clear

Computer has these codes to use:
P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected

P1504 Idle Air Control Circuit
P1505 Idle Air Control System At Adaptive Clip
P1506 Idle Air Control Overspeed Error
P1507 Idle Air Control Underspeed Error
P1508 Idle Air Control Circuit Open
P1509 Idle Air Control Circuit Shorted
P1510 Idle Signal Circuit

Yet No Codes set
Which makes me think computer software issue, computer is ignoring overspeed because its setting the higher RPM

If you want you can swap out clutch switch, easy to do
Its 3 switches inside, each with two wires
All 3 Switches are CLOSED when clutch pedal is down all the way, and open when its up even a little

 

I ran it without the IAC and i had the MAF unplugged when i was spraying the upper clinder lub into the throttle body. The check engine light did come on and it did record codes which i cleared after i was done.

 

Conclusion:
The computer CAN see "problems"
And the Computer doesn't think the high RPMs are a problem