1996 Ford Ranger 4x2 (Splash)

[DavidW]

D

I did it a couple of times, the spring never moved, the IAC just made a little "pop-type noise" like it was trying to do something. It appeared to be stuck trying to move.

Replaced IAC Valve, Throttle Body Sensor, Spark Plug Wires and Air Filter. All new parts. Sprayed MAF Sensor with MAF Cleaner. Still idles rough. RPM's goes down to abt 500. I think the MAF Sensor is next.

 

[RonD]

Something else is wrong, I know, DUH

The computer sets the idle RPMs using the IAC Valve, this is not like a set screw where its a fix idle
The computer has the RPMs from the crank sensor and has "target idle RPMs" in its memory based on engine temp(ECT sensor)
Cold idle should be about 1,100rpm
As engine warms up idle drops, computer closes IAC valve bit by bit
Warm idle 750rpm, for automatic trans, manual trans is 625 usually

Computer adjusts voltage at IAC Valve to open it and close it, and its accurate +/-3rpm
Which is what I mean by something is wrong, lol.

MAF sensor can certainly cause a bad air/fuel mix, but idle wouldn't change, computer would just open IAC valve a bit more and try to stabilize it at its "target" RPM, computer is very responsive with IAC Valve voltage.

IAC valve gets 12volts on the red wire with Key on
The other wire(White/blue) is the Ground but at the computer(pin 83), computer pulses the ground to lower voltage closing the IAC valve a little at a time
This is a very accurate way to control voltage

If RPMs are dropping to 500 then computer is not controlling IAC valve, maybe bad wire?
You can use sewing needle to pierce the IAC valves wires, then use a volt meter to see the voltage going to IAC valve, with key on, and then engine running, generally 8 to 11volts, lower voltage lower RPMs

 

[DavidW]

Something else is wrong, I know, DUH

The computer sets the idle RPMs using the IAC Valve, this is not like a set screw where its a fix idle
The computer has the RPMs from the crank sensor and has "target idle RPMs" in its memory based on engine temp(ECT sensor)
Cold idle should be about 1,100rpm
As engine warms up idle drops, computer closes IAC valve bit by bit
Warm idle 750rpm, for automatic trans, manual trans is 625 usually

Computer adjusts voltage at IAC Valve to open it and close it, and its accurate +/-3rpm
Which is what I mean by something is wrong, lol.

MAF sensor can certainly cause a bad air/fuel mix, but idle wouldn't change, computer would just open IAC valve a bit more and try to stabilize it at its "target" RPM, computer is very responsive with IAC Valve voltage.

IAC valve gets 12volts on the red wire with Key on
The other wire(White/blue) is the Ground but at the computer(pin 83), computer pulses the ground to lower voltage closing the IAC valve a little at a time
This is a very accurate way to control voltage

If RPMs are dropping to 500 then computer is not controlling IAC valve, maybe bad wire?
You can use sewing needle to pierce the IAC valves wires, then use a volt meter to see the voltage going to IAC valve, with key on, and then engine running, generally 8 to 11volts, lower voltage lower RPMs

So are you saying the crank position sensor maybe be bad? I guess I'm confused since I'm not any kind of mechanic. Thanks again for all your help.

 

[RonD]

No, I am saying with new IAC valve idle can not drop to 500rpm unless power is cut to IAC valve

 

[DavidW]

Ok,

No, I am saying with new IAC valve idle can not drop to 500rpm unless power is cut to IAC valve

Ok, thanks for that info. What's your recommendation where I should look?

 

[ericbphoto]

Ok,

Ok, thanks for that info. What's your recommendation where I should look?

That would be the part where he said to Pierce the wires to the IAC with sewing needles or pins so you can connect a meter
to the needles and see what voltage the IAC is getting.