88 2.3 ranger super high idle. no vacuum leaks. good IAC.

[03ranger4x4]

Basically what the title says. Just bought an 88 2.3 and when warm will idle super high, from the sound like 2200 rpm. Unplug iac, engine stalls. If I remove the IAC hose, I can throttle the air with my thumb and get it to idle perfect. So I think the computer is commanding the high idle for some reason. Can't figure out why. Cleaned the IAC didn't help. Anyone have ideas?

 

[RonD]

If you can control(reduce) the idle by pinching off the IAC Valve's inlet hose then IAC's step motor is most like like bad.
Computer controls the IAC valve by sending voltage pulses, like a Morse Code, to the Step Motor, different pulses cause the motor to "go to" a specific place, there are approx. 100 'steps' the computer can use to set IAC valve to get the idle it wants.

Yes, computer could be bad, but it is most likely the IAC Valves step motor.

 

[03ranger4x4]

It might be the IAC motor itself. But the reason I was thinking the computer was actually making it idle high was because the motor stalls when you unplug the IAC itself. I mean, the motor has to be working to some extent or else if it was 100% dead the engine should act the same weather it's connected or not. If I find my darn obd1 scanner today I'm going to pull codes to see if maybe a sensor is screwed up. A lot has scared me so far of the previous owner of the truck. My firing order is exactly opposite of what it should be....what's normally cylinder #1s plug wire goes to 4 on my truck or it doesn't run. Last owner said his grandson did the timing belt, so he definitely didn't do it by the book. Kinda makes me cringe to think about...I'm actually curious if my cam is even timed right.

 

[Dale_K]

My recently purchased 06 2.3 sometimes does the same thing but a lot of the time it's perfect. Like you I'm trying to figure out if the valve is bad or some kind of sensor is giving the ECU bad info. Disconnecting my IACV kills the motor when it's idling too high and tapping on it gently with a hammer didn't free it up.

I don't have a scanner that will give me the raw sensor values. One thing I've noticed is that after the motor warms up, shutting it off and restarting causes it to idle perfectly. A new IACV is about $60 for a Chinese unit and so far I'm debating on whether to spend the money on a valve I don't think I need or buying a scanner that would let me see the data.

The only inputs I can think the idle system might use are the rpm (assume this comes from the crankshaft sensor) and whether the A/C is on. Mine seems to act weird after a cold start when I can hear the mechanical fan engaged like the A/C has been commanded on briefly. I understand Ford has a thing called CASS for computerized anti-slugging strategy, that runs the A/C for a few seconds after every cold start (8 hours since last start).

Post up the follow-up if you figure it out or if you try a new IACV. I took mine apart a couple of times and there is no dirt in it at all and the plunger seems smooth and the rubber seal looks perfect.

 

[03ranger4x4]

My recently purchased 06 2.3 sometimes does the same thing but a lot of the time it's perfect. Like you I'm trying to figure out if the valve is bad or some kind of sensor is giving the ECU bad info. Disconnecting my IACV kills the motor when it's idling too high and tapping on it gently with a hammer didn't free it up.

I don't have a scanner that will give me the raw sensor values. One thing I've noticed is that after the motor warms up, shutting it off and restarting causes it to idle perfectly. A new IACV is about $60 for a Chinese unit and so far I'm debating on whether to spend the money on a valve I don't think I need or buying a scanner that would let me see the data.

The only inputs I can think the idle system might use are the rpm (assume this comes from the crankshaft sensor) and whether the A/C is on. Mine seems to act weird after a cold start when I can hear the mechanical fan engaged like the A/C has been commanded on briefly. I understand Ford has a thing called CASS for computerized anti-slugging strategy, that runs the A/C for a few seconds after every cold start (8 hours since last start).

Post up the follow-up if you figure it out or if you try a new IACV. I took mine apart a couple of times and there is no dirt in it at all and the plunger seems smooth and the rubber seal looks perfect.

Your fan is loud on a cold start because it used a viscous fluid clutch. This fluid gets thick in the cold and will not slip right away until it has time to get moving. The fan is dumb so to speak. It grips when hot air passes over it, slips when cooler air passes over it. The ecu has no control over the fan speed. Anyways, my 88 ranger is night and day compared to yours. I don't even have a MAF on mine, it's the old speed density setup.very old school indeed

 

[RonD]

The motor holds the Valve open, when there is no power, like when you pull the wires off, the valve closes on it's own.

Engine can stall at that point, but on some throttle linkages there is a TPS(throttle position sensor) adjustment screw(looks like idle screw on carb), it can be turned so engine doesn't stall with IAC unplugged
You want idle to be 500-600 but no higher with IAC unplgged.

 

[03ranger4x4]

The motor holds the Valve open, when there is no power, like when you pull the wires off, the valve closes on it's own.

Engine can stall at that point, but on some throttle linkages there is a TPS(throttle position sensor) adjustment screw(looks like idle screw on carb), it can be turned so engine doesn't stall with IAC unplugged
You want idle to be 500-600 but no higher with IAC unplgged.

Yeah, exactly. The computer is telling that idle air valve to be open....but when I unplug the connector on the iac and the engine stalls that is showing my that the iac is no longer being held open and springs closed.
If the IAC motor was bad, it wouldn't change position when I disconnected it. In fact if it was bad, it should act like it's unplugged all the time. Right?

 

[RonD]

No, IAC motor could be misreading the commands from computer

 

[03ranger4x4]

No, IAC motor could be misreading the commands from computer

Have you ever seen one go bad like that before? I mean the Iac is literally just one coil of wire....do you know how many ohms a good one should read, I have a multimeter. The Iac as far as I see it is
just a solenoid that gets a pulsed voltage to it to make it pull harder or weaker on the valve inside. I just really don't want to drop 20-30 bucks on something that works fine. No to mention it only seems to idle very high when the engines hot. Cold it's still high buy not as high...for what that's worth

 

[RonD]

Yes, there would be no way to tell easily if it is the IAC valve or Computer control.

It has been my experience that the moving part tends to be the part that is at fault.
But that won't be 100% of the time.

Since your computer is not turning on CEL to report unresponsive IAC Valve or no RPM issue, the computer could be at fault

 

[03ranger4x4]

Yes, there would be no way to tell easily if it is the IAC valve or Computer control.

It has been my experience that the moving part tends to be the part that is at fault.
But that won't be 100% of the time.

Since your computer is not turning on CEL to report unresponsive IAC Valve or no RPM issue, the computer could be at fault

Yeah, I dont even have a check engine light. lol... I managed to pull codes just a while ago and I got code 67 for the on demand codes...which is simply becuase I left it in gear during the test. No other codes for that portion.

For the memory codes I got code 63, which is TPS voltage low. Which I am honestly going to blame my rigging of the trottle plate screw to get it idle without the IAC on that.

And I THINK I saw code 14, but it was getting dark and I am just using a muiltmeter to check the codes. But anyways, 14 indicated erratic PIP signal. Which kind of worries me as the truck once in a blue moon will just off and may or maynot start back up right away. Previous owner said the TFI module was replaced...which make me wonder if they put the heat sink compound on it correctly. With the firing order being the way it is from when they did the timing belt, I wouldnt be surprised if they put none on it.

 

[RonD]

Well the PIP is the RPM reading for the computer.
So at 2,000 RPM the computer might see 600 RPM

In that case IAC and computer would be OK, issue would be incorrect PIP signal

 

[03ranger4x4]

The idle issue seemed to go away on its own. Now the truck is bucking and misses randomly when warm. I looked at the tfi module and found out one screw was stripped that holds it to the dizzy and there was NO thermal paste on the module. So I went ahead and bought a new tfi, and thermal paste and put teflon tape on the stripped screw and everything is in order there now. But the random engine cutout remains. I think I'm going to pull the computer and open it up to see if things are corroded or out of order. Other then that my only guess is the pickup coil in the dizzy is going bad. I pretty must played jump rope with the harness while it was running and nothing I did made it miss or stall.

 

[03ranger4x4]

Well the PIP is the RPM reading for the computer.
So at 2,000 RPM the computer might see 600 RPM

In that case IAC and computer would be OK, issue would be incorrect PIP signal

You know, that's an interesting idea....I'll have to look into it. How often have you ever seen a distributor pickup coil go bad? I guess that or an actual internal issue with the computer is about the only 2 places I have to look now for this random cutting out issue.

 

[03ranger4x4]

Well the truck officially died on my today...lucky it was close to my dad's place and he was able to pull me to his place. So while I was on the side of the road I disconnected the computer and in doing so one of the pins for the computer pulled out with the connector. I'm really hoping that was the issue all along, just a corroded pin that wasn't getting a good connection. I'll see when I open it up and try and solider that pin back in