I have a 2000 Ford Ranger 2.5l engine.
When I start it the motor goes nuts. The idle is way out of whack. When I shift, stop, go.
I have read the 98 to 2000 are known to do this.
I have done everything I can including take it to a mechanic. 26yrs with ford and shop manager.
Still doing the same thing.
I have replace the IAC-TPS-Air Mass all twice.
I have no air leaks.
Taken Throttle Body off and Cleaned.
Pvc Open
Ford Forum.
Internet.
Please has anyone found the problem. Please take note of all I have tried.
Desperate.

 

I used a free app called fordsys scan. Using the bluetooth obd2 dongle I got off of ebay I was able to use the app to access the pcm and have it calibrate the idle. I believe in the app it's pcm--->koer
Here's the link if you want to read up on it.
Hope that helps.

 

Welcome to the forum


I guess the first thing to do is to see if the computer is causing the high or erratic RPMs or a mechanical problem is.

Warm up the engine, 5 minute drive should be fine, longer is fine as well.
Leave engine idling and open the hood
Unplug the wires on the IAC Valve.
IAC Valve will close all the way and engine RPMs should drop to 500, or engine may even stall, either is good, it means no vacuum leaks.
And your wild RPM shifts are from the computer

If RPMs stay above 700 then there is an air leak.
OR....someone has messed with anti-diesel screw on throttle linkage, it looks like an idle screw but fuel injected engines can't use an idle screw so that is NOT what it is.
If this anti-diesel screw is holding open the throttle plate then unscrew it until RPMs are at 500 or so with IAC Valve unplugged.

Air is what increases engine RPMs not fuel, if you add more fuel you just get a flooded engine, but if you add more air you get higher RPMs.

Thats how the IAC Valve works, computer opens it to increase RPMs and closes it to decrease RPMs, in essence a controlled vacuum leak.

 

I have replaced everything. And when I disconnect the IAC it slows down.
So I will try another computer and see what happens.

I do appreciate all your help.

 

Engine must be warmed up for the test or it will always drop RPMs when you unplug the IAC valve.

If engine was warmed up then yes the PCM(computer) was holding the IAC Valve open to keep RPMs high.
The PCM is not smart, it is basically a calculator, no more than that.

If it is holding RPMs high then it has a reason to.
I wouldn't buy more parts.

I would get an OBD2 reader.
A Bluetooth OBD2 interface can be used wirelessly with smart phone or tablet.
You can then see what the PCM is seeing, RPM, coolant Temp, MAF air flow, O2 sensor, ect....in Real time