Long time lurker, very few if any posts.

So I have a 2000 3.0 2wd xl ranger. Base. No cruise. No power windows. Nothing. I have the idle air control disconnected for probably 3 years because of excessively high idle. 1000 with tax compressor engaged, 1500 without the compressor running. I changed the evap service port valve thing recently and reconnected everything. No change other than the canister purge actuated every 10-15 seconds. Disconnected that too, back to status quo. My vents all work fine, no vacuum loss on acceleration. I have changed the idle air controller about 5 times with motorcraft parts from Amazon with no change. Great help for this would be appreciated.

No codes reading when everything is connected. When disconnected just p1504 and p1507. Iac circuit fault and iac duty cycle lower than expected.

thank you gents!

 

3.0l manual trans should idle when stopped with warm engine at 750-800rpms

So with engine warmed up and IAC valve unplugged you should see about 600-650, or engine will stall, either is OK
Extra Air = higher RPM
Extra Fuel = flooded engine

So its extra air
The throttle plate sets base RPM(assuming no "leaks"), on some engines there is an anti-diesel screw on throttle linkage, looks like an "idle screw" but fuel injected engines can not have an idle screw, so its an anti-diesel screw, lol
See if you have one, easy to see on the linkage where throttle cable attaches
With warm engine idling(IAC Valve unplugged) turn the anti-diesel screw counter-clockwise and see if RPMs start to drop, if so keep turning until engine is barely running, 600rpms
Plug back in IAC Valve and RPMs should go up to 750-800

If there is no anti-diesel screw or its already "backed out" then air is coming from elsewhere
Its possible the throttle body is the leak, not hard to take it off and clean it and replace gasket, and check that throttle plate is closing all the way

The TPS(throttle position sensor) can hold the throttle plate open a bit, especially 3rd party TPS, you can shut off engine, remove the TPS, and then restart engine to see if idle has dropped

With warm engine and IAC Valve unplugged and idling at higher RPM, start unplugging the larger vacuum hoses from upper intake, Power brake hose and then PCV hose and cover that open port with your finger, if RPMs do not drop then replace the hose and move to next hose until you have done all the vacuum hoses

Since you are not getting Lean codes and should with even a smaller air leak, if could be computer issue
But it is setting codes with IAC Valve unplugged so seems to be "sane"
So I wouldn't think computer issue since unplugging IAC Valve takes computers RPM control away, but it still has Spark Advance and fuel mix control which can raise RPMs a bit

If you have an OBD2 reader you can look at sensors to see what the computer sees, i.e. current RPM, MAF data, air temp data, coolant temp, fuel trims

 

thank you very much for the reply Ron, I’ll try to respond in line with the questions and information you have me.

so engine idles at 1000
when AC kicks on it surges to 1500 and then over 13-15 seconds it slowly dips back down to normal until the compressor kicks off.

unplugging IAC causes stall when engine cold and very low rpm when warm.

I’ll try the TPS and report back. Thanks again.

i also attached some data points on the vehicle from my scanner.

 

Engine must be warmed up when you unplug the IAC Valve or it will always stall

Yes, AC compressor coming on should always increase idle RPMs but only by 50-100rpms

No use hooking up an OBD2 reader before coolant temp is above 150degF
Computer ignores most sensors when in Open Loop, Open Loop = coolant under 150degF
Once engine warms up computer will check the sensor data and use the data calculate air/fuel mix on the fly, Closed Loop = coolant above 150degF

-5% to +5% short term fuel trims are normal

O2 bank 1 sensor 2 is the O2 sensor after the cat converters, its voltage is low, should be 0.75 to 0.85v not 0.3v
And 99.2% means no connection to O2 so odd to see 0.3v and 99.2% at the same time
Check the wiring at that O2 sensor wires can melt if they touch exhaust or Cat


Just FYI
O2 sensor "1" are upstream sensors closest to the engine
On a "V" engine there will be two of them, Bank 1 Sensor 1 and Bank 2 sensor 1
Often abbreviated B1S1 and B2S1

O2 sensor "2" are downstream sensors, after Cat Converters
Most vehicles have a single exhaust pipe going to the rear, so only have one O2 sensor after Cat, Bank 1 sensor 2, B1S2
All the O2s are the same sensors just different positions in the exhaust system

Dual exhaust and some later models can have Bank 2 sensor 2, B2S2

 

Thanks again Ron,

I attached an operating temp idle with everything plugged in. The wires “appear” intact for all 3 sensors. As far as I know they are all original or have 140k miles on them. I bought it when it had about 100000 miles on it.

 

O2s should be changed after 12 years or 100k miles, they will cost you money on lower MPG after that

B1S2 is for sure bad, change all 3

See if you can find the IAC Valve voltage and the Throttle sensor %
Key on engine off
Throttle closed = 16% to 19%
Throttle wide open = 90%-92%

Key on engine off
IAC valve voltage 11-12volt
Engine idling(warm) 7-8volt

 

thanks again,
are those values for key on engine off? It notes engine idling, confused on that part

 

For IAC there are two, key on engine off and then engine running
Computer opens IAC Valve all the way for start up, so over 11volts
Then after start up if closes IAC Valve to set idle RPMs

TPS doesn't need engine running just key on

 

sorry for the delay,

I have plenty of voltage meters. How do I read the IAC and TPS voltage?

 

When testing a wire that is connected to a device I use a sewing needle to pierce a wires insulation, push it in an an angle so it holds better
You can also buy "Needle Probe ends" that attach to current probes that allow you to pierce a wires insulation
No, this does not hurt the wire or insulation

But if you have a OBD2 reader, which it looks like you do, just look up the IAC Voltage and TPS %, key on engine off, and then engine running

 

Duly noted.

I do have the throttle percent, but no IAC voltage option. I do have the needle probes for my multimeter, that was my guess as to what I would have to do. Ill report back tomorrow. For reference, I changed the back O2 sensor, not the front ones, those are on order.

As always, thanks a ton.

- Frank

 

So I just tested the voltage on my IAC. The red wire I probed and left the black wire on the battery negative. It seems to be getting 14+ volts all the time. Throttle opened or closed.