Hi guys...I have a 94 3.0 Ranger XLT, auto xmission, 92,700 miles.
I have been working on it for the past week. I replaced the fuel filler neck hose, the fuel filter and clean up in general.

In the recent past I have had an idle problem with surging both at idle and cruise. I cleaned the MAF sensor and the IAC Valve, which was full of carbon and pretty nasty, and throttle body.

After that it seemed to run fine for several hundred miles. The idle was fast for a few minutes then dropped to normal idle speed. if I turned on the AC the idle speed picked up a few RPM's. Then recently it started surging again.

So after I changed the filter and filler neck I cleaned the IAC valve again with CRC throttle body cleaner and an acid brush. Now the idle is very low to the point where it stalls frequently when its cold. After it warms up, the idle is more stable but still low, and turning on the AC has no affect. I suspect the IAC valve is the problem again...maybe its just worn out.

Does the ECU take a few miles to read the IAC valve or is that a none issue? I dont have a check engine light and the truck seems to run okay on the road. Your thoughts please?

I might add that the fuel filler hose has been cracked for over a year. I could put gas in the truck but not fill it. Also the filter hasnt been changed for several years. I dont know what filter came out of the truck. All I could read on the filter was" 0321" and "canada". I saw no mfg name on it. I installed a Wix 33097.

 

When you turn the key on the computer will open the IAC Valve all the way for starting the engine.
So without touching the gas pedal, when you start a fuel injected engine, RPMs should go up above 1,500 then drop down
If engine is cold idle should be above 1,000, colder the temp, higher the idle
As engine warms up idle will start to drop
Target idle for warmed up engine on manual trans is 650, automatic 750

Yes, when you put automatic in gear RPMs might go up 50, or when you turn on the AC, that is the IAC valve being opened a bit more by the computer

Computer detects engine temp using an ECT(engine coolant temp) sensor, this sensor has 2 wires and is only used by the computer.

There is also a 1 wire ECT SENDER, it is only used by the dash board temp gauge

These are both located next to each other on lower intake front of engine, under throttle body.
So maybe you unplugged the ECT sensor?

From your description the IAC is unplugged or unpowered, it should have 12volts with key on, computer uses PWM(pulse width modulation) to set IAC valves position.
Remove IAC valve, turn on the key, plug IAC Valve wires in and valve should open all the way, unplug the wires and it should close all the way, test it a few times

 

Ron...Outstanding! Thanks for those specific details. I checked to be sure the IACV connector was properly plugged in....looked at the wires for obvious damage and corrosion...everything appeared to be okay.

I'll check that 2 wire ECT wiring for connection too. So if the key is on and 12V to IACV from the ECU, I should be able to read that with a meter right, or would the pluses be too minute to see without a scope?

I will remove the IACV and do the key "on" test you suggested to see if the valve opens and closes.

This valve is OEM with 91700 miles on it. Do you know if there is an average life span for this unit? There seems to be a lot of talk here about these valves being problematic.
Thanks again Ron...I'll be back with the results later in the day

 

Hi Ron...back with ya. I checked connector and wires at the two wire ECT sensor. All looked good, clean and solid. I turned the key on & checked the voltage to the IACV with my meter set on DCV. I got nothing. Went to AC/PDC and watched it go from 12 and count down to 1.2. Must be that pulse width voltage you mentioned....or not.

Then I removed the valve and did the key "on" check. I watched it for several minutes. The valve never opened but I could feel the motor housing (solenoid?) getting warm in my hand. When I nudged the plunger with a screwdriver it "popped" opened and stayed open. The initial movement was very jerky, like something was sticking or the motor was too weak to open it. I turned the key off and the plunger stayed open so I reinstalled the valve

I tried to start the engine to see if the plunger staying open would increase idle RPM. At that point I got sidetracked. The engine turned over but no start. Checked the pressure in the fuel rail thinking I had a bad filter or my pump had quit too...there was no pressure. I pulled the fuel pump relay and swapped it with the WOT relay. I turned on the key and the spray from the fuel rail hit the bottom of the open hood...plenty of pressure now. This is the second time that has happened in 3 months.

The engine fired right up but the idle was still way low. Engine temp or AC on/off had no affect. Idle was so low that the alternator showed 12volts or less until I revved up the engine...then went to 14.3.V. Hard to believe that the engine would be able to idle that slow.

I drove the truck around for a few miles to warm it up. it seemed to accelerate and run fine except when I was coasting to a stop. From 25 MPH to full stop, foot off of the accelerator, the amp meter was fluctuating 12 to 14V. During that time I suppose the engine was in idle mode and that would explain the fluctuation.

I am leaning toward a bad IACV. What do you think?

When this is done I'll continue with the "restoration" my truck. I have kinda far to go. I think the fuel pump relay issue will be next. I seem to remember a thread about an intermittent start problem with a relay. Then next, the O2 sensors. My fuel mileage sucks..12-13 MPG. Everything on this truck is original except for the brakes and headlights.

Thanks Ron

 

Yes, reads like IAC valve is obviously sticking.

If you pull it off again I am sure it will be closed again, if idle was that low, should be 1,500+ with wide open IAC valve

My '94 still has original IAC valve, 22years old and 350k miles, also original fuel pump, knock on wood, lol.

 

350K miles?? Wow . Yep, knock on wood for thing with those miles. By that standard mine is nearly new! LOL Gotta love these old rangers. Too bad Ford stopped making them.

Okay Ron...I am off to get a new valve. Looks like OReilly auto has a BWD unit for $47.00. Only physical difference is the connector is on the end of the motor instead of the side like the OEM. I think I have enough harness to reach though. I'll let ya know how it turns out.

BTW, I wanted to ask, what is that **** button looking thing on the side of the IAC valve. Is that a relief valve...an adjustment ****?? Just curious as to its function.
Thanks a million for your expert help Ron. I appreciate it.

JD

 

That black cap just pulls off and snaps back on, it has a filter on it.
It covers an air vent, it allows the valve to slide in and out without air being trapped behind it, so pressure relief would be a good term.

Unhook the battery while you are gone, then after installing the new IAC valve hook battery back up.
Can take a few drive cycles for computer to learn IAC valves settings, so wandering idle may be noticed, but it should be high on cold start and then drop as engine warms up, that part should be instant.

 

Okay...got the valve replaced and the harness was just long enough to connect to the end connector on the new valve. Truck started right up and idle was higher...high enough to keep the alternator charging but I dont think it was 1500 RPMs. I turned on the AC and the RPMs picked up a bit too. Idle seems stable now in the garage. I have errands to run tomorrow so I'll see how the truck runs then.

Ron, I left the house before I got your last post so I didnt disconnect the battery while I was gone. Could that pose a problem? Should I back up, disconnect the valve and battery both for 10 minutes or so or just let it ride??

I hope in a few days it will all be back to normal again.

 

It will be fine, just takes computer a little longer to see that the old PWM pulses aren't repeating same RPMs they did before, computer then adjusts for that and if repeated a few times it then overwrites the old pulse setting with the new.

When you clear the the memory then computer uses Factory settings, but knows it needs to "learn" new settings, so remembers settings as it goes, just a little faster, I wouldn't worry about it.

 

Great! Ron thanks again. I really appreciate your help and technical explanations. I am sure we'll be talking again soon. This is a great forum and great members who are willing to share their knowledge. I am happy to be here.

Have a great day
JD

 

Thanks

And thanks for posting follow up of what you are doing.

Many questions get answered here but there is no follow up of the results so you don't know what worked and what didn't

 

I know what you mean. I will never do that as it defeats the purpose of the forum. Besides, as you say, you'd like to know what worked and what didnt. I'll keep the board posted on my progress and problems.

FYI, I drove the truck around for a few miles this afternoon. You were right. The more I drive it the better it runs. Idle speed is good in all ranges now, cold and warm, AC on or off. The idle is smooth, the RPM surging is gone and the truck is running very well. While sitting at a traffic light with the AC on, the idle was so smooth I wasnt all that sure the engine was still running! LOL I'm happy...