Hello, i have a 2003 4x2 Ford Ranger with the 2.3 engine that, when i remove the IAC connector stays put at 600-650, i reconnect the IAC stays there, if i accelerate keeps at 2000rpm and stays there, if i remove IAC connector again, idles and reconnect stays at idle..

I have changed the IAC and the problem continues, what could it be.

 

Welcome to the forum

Start cold engine, should idle at 1,000rpm or so, Choke is On
Unplug IAC Valve, RPMs should drop and engine will probably stall, depends on outside temp, but in any case if idle drops you will know the computer was in control of it at that time, so wiring is OK

IAC Valve should have 12volts on one wire with key on, often red wire
The other wire goes to the computer, its a variable Ground, computer varies the ground to set idle RPMs based on engine temp, from CHT(cylinder head temp) sensor
CHT sensor is located between the #3 and #4 spark plug holes on the 2.3l Duratec, these could read wrong temp, higher than actual, so lower idle than it should

You can get a Bluetooth OBD2 reader for under $20, like ELM327 which you can use to view live data from sensors, works on ANY vehicle made after 1995, good tool to have

Ford uses a true solenoid IAC Valve so it can only be replaced with Motorcraft or Hitachi brand IAC Valve, just FYI, better to get a used one at wrecking yard than 3rd party brand for this part

Assuming manual transmission
600-650 seems low for warm idle on a 4cyl(I4) engine, as they tend to vibrate under 750rpm because they only fire every 180deg

Also there is an emission's requirement on manuals, RPMs must stay above 1,000rpms until speedometer is below 5MPH, under 1,000rpms(idle) causes more pollution than at 1,000rpm
Also when shifting the RPMs should hold high, if you shift to neutral or just leave the clutch pedal down, after 7 seconds or so idle should drop to around 1,000 if still above 5MPH
The RPMs staying high when shifting also save on fuel

 

Thanks RonD, i will try and see what the computer is doing with and OBDII reader. Issue is even when shifting rpm's are between 2000 to 3000rpm

 

RPM shouldn't go up when shifting, but won't drop when you push in the clutch

 

will try to updload a video later, but its kind of weird, if i push back the throttle plate, it will lower the idle speed, seems like i need a OBD2 scanner to see that the computer its doing.

 

Read like throttle body needs to be cleaned

 

Already did, this is driving me nuts

 

If throttle plate is not closing all the way or if wiggling it causes idle to drop then there is an issue there

The total and ultimate control of a gasoline engine's idle/RPM is air
If you add more gas you get a flooded engine, if you add less gas you get a pinging/knocking engine

So air flow is RPM control

Spark timing can also change RPMs, but on a 2003 you have 0 control over that, OBD2 reader will show spark timing and you could see if its jumping around

 

I agree with everything Ron mentioned.

On the 2.3 DOHC, the intake from 2001.5-2003 will have an IMRC system. This stands for Intake Manifold Runner Control. Basically its a couple of butterfly flaps in your intake runner, that open or close to "increase/decrease" intake runner size. The idea is to increase air tumble at specific times, and increase air flow speed by making the hole the air passes through "smaller"

That being said, the system has a shaft that runs from end to end, very close to the flange of the manifold (where the flaps are, internally) On the Cyl 1 end is a plastic plug, that you can sort of make out if you look at the runner flange directly behind the power steering pump. If there is what appears to be a large hole there, or you can see a metal shaft, you need to take the intake manifold off and replace the cap, or otherwise seal that end. There are a lot of threads out there that pertain to the issue, but here is a picture of what you are looking for. This plug can cause idle issues and "idle hunt" as it is a leak that only really "effects" one single cylinder.

IMRC/Intake Manifold Leak




FWIW, the idle should be between 900-1000 RPMS when warmed up. They don't like to idle much lower than that, and it just starts to chug if it is reduced. The IAC valve will compensate for any air leaks but may hang if it is gummed up. The IAC is a PWM style unit so once its unplugged it will close, like Ron stated.

 

Ok, i removed the manifold, changed CHT temperature and Temperature sender, no leaks on manifold, changed all gaskets, replaced IMRC solenoid and connector and no change on the idle issue, and i am thinking i am having a short on the harness, this car harness was cut by vandalization, i have ordered an used ECM harness to replace the harness.

Engine yoyo's itself and if i connect the IAC stays at 3000rpm

 

Yeah, the fact that the IAC won't respond at all except to peg full speed sounds like its a wiring problem IMO. It's possible that there is some other vac leak, but since the idle drops to ~650 and chugs when it's disconnected tells me that this is a commanded idle RPM, either by the ECU or by a ground fault.

A high quality OBD2 scanner with "deep access" like a SOLUS can manipulate idle by commanding it via ECU through the scan-tool. If you can get your hands on that, you can see if the ECU can even "communicate" with the IAC.

 

Yes, i was actually disconnected the IAC and measuring voltage at the terminals, but even with the IAC disconnected, the engine is not stable.

 

At this point I will assume your issue might lie with the damaged harness. Hopefully it has not caused issues with the engine ECU

 

Update on this: TPS reading at idle shows 99%, probably some other short on the wires on mixed signal from the bad harness, i am waiting for the harness,

removed intake manifold during the weekend and replaced all the gaskets on the intake manifold, replaced imrc as the scanner was showing imrc valve stuck open.

 

IAT reading shows -40 celsius, there is the intake air temperature sender, i have found none

 

IAT sensor is in with the MAF sensor, two outside wires on the 6 wire connector are for the IAT(intake air temp)

Unplug the 6 wire connector and test the outside 2 pins with OHM Meter, chart here: https://www.freeautomechanic.com/ima...ting-chart.gif
-40 could be the default value of no sensor connected
Also test each of the outside wires with Volt meter, KEY ON, one should be 5volts

Yes, should be 17-19% reading from TPS at idle, 99% should never be seen with sensor connected, its a default reading when TPS is not working/connected, O2s have the same 99% default and a few other sensors
TPS is a 5volt sensor, like all the other sensors, should show just under 1v when throttle is closed, 1 volt is 20% of 5volts so, 17-19% would be expected
Wide Open Throttle(WOT) should be 4.5v, that's 90% of 5 volts, so 99% would/should never come up
If the 5v power wire was shorted to the return wire, maybe, but never seen that before

Test the 3 wires at the TPS, key on, one should be 5volts
Not having 5 volts at these two sensors could mean a splice connection has broken, and would account for the -40deg and 99%

 

yes, surely this is a wiring issue

 

A little update here, changed ECM wiring harness, problem solved. Truck is running fine, 228900 miles and no oil consumption, steady idle, nice machine