Idle problems?

[Garyww2]

Hello everyone,

I suspect I may have some idle issues on my 2007 Ford Ranger. It is a 4L V6 with a manual 5 speed transmission. This is my problem;

I had recently fueled the truck up, everything ran fine until I went to slow down to turn off the highway to work, as I took the turn the truck stalled on me. I was able to get it restarted after the turn and after that the truck started to idle very low (500 rpms) and at times wanted to stall, subsiquently idling a bit rough too (I suspect however that was the imminent stall). Ran some seafoam through it, drove it, ran another tank of gas through it, and now I have noticed that the RPMs are rather high; out of gear it stays at 2000, and then, rather suddenly, drops to 1500 or so, and then slowly works its way back up to 2000 until I come to a complete stop, at which point it will work its way down to 750.

Thus far I have cleaned the MAFS, the TB, the air filter, replaced the IACV, cleaned the connector for the TPS, and replaced the fuel filter. I also disconnected the battery and let it sit for 10 min. First I have seen it stick to 2 grand when its out of gear. Always seen it drop down to at least 1000, if not 750. Note; I have yet to replace the PCV valve, it is due but I am doubtful to think that would cause this? Suppose thats why I am on here...

Truck has 321,000 KM and ran fine up until now. Other than the RPMs, truck purrs like a horny kitten. No codes have been thrown

 

[RonD]

Welcome to TRS

PCV Valve can cause that, just FYI, PCV is a controlled vacuum leak, but not a monitored leak, lol

After engine is warmed up and idling
Unplug the IAC Valve's 2 wire connector
RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leak
But it also means Computer(PCM) was setting the high idle, if it was above 1,000rpms

You can only use Motorcraft or Hitachi brand IAC valves as replacements, just FYI, other brands will cause odd issues
Better a used Motorcraft from wrecking yard than new anything else

There should be Codes, PCM sets idle and has "target idle RPMs" based on engine temp
P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected

Its possible the ECT(engine coolant temp) sensor is acting up, so computer would idle high (thinking engine is cold)
Its just a resistance sensor, 5volt in and 3volts out if cold and under 1volt if warmed up

But other than that you could be looking at a PCM issue

You can get an OBD2 Bluetooth Reader for $15-$20, works on any vehicle 1996 and up so not a ranger or even a Ford tool, works on all vehicles
And then you can see what the computer sees from each sensor
This can help you narrow down why computer is doing what its doing, and WAY CHEAPER than guessing what might be wrong and replacing parts

 

[Garyww2]

Hey thanks for the welcome!

And only the best parts for my Ranger! Most, if not all the parts I use I go for Motorcraft or an equivilent brand. No skimping out on parts, most of the time it just causes further headache down the road. Just need to order in another PCV valve, I guess mine is electrically heated.... who'd thunk?

If I am not mistaken I did see that on another post! Evidently I could not find it. I did do that, and it did drop..... 100 RPMs (750 to 650), then once plugged back in it ran itself back up to 1000. No vaccum leak from the sounds of it. Thankfully lol

And I will check with the scanner and see what it is seeing, I think I have one somewheres at home. Perhaps it's hiding the code, no check engine light as of yet. I will also read into testing the ECT and see if that is gone sour or not. I mean, if you keep throwing parts at it it'll eventually fix it right?

But oh boy, a PCM. Sounds expensive and a real pain to deal with haha

If I find something I'll post it, going to work on it later tonight

 

[RonD]

Actually throwing parts at an engine issue can muddy the waters when trying to find the actual issue

Unplugging and plugging back in sensor wires is a good place to start, it cleans the contacts
Most of the time a new sensor didn't fix the problem, you just had to unplug it and plug in the new one and that fixed the problem

Most sensors run on 5volts so a little corrosion on electrical contact changes things ALOT
O2s run under 1 volt

So yes, watch some Live Data to see what computer is seeing and why its setting a high idle sometimes
As the computer guys say, "garbage in = garbage out" so computer needs accurate data

 

[Garyww2]

So what should the measurements be on the ECT? I am getting 16,000 ohms cold at the sensor. 9.8 volts to the sensor itself. Thing isnt in the best place (found it under the throttle body next to the thermostat housing). Also; ran the OBDII; pending code was P0511, DTC (?) Has a ECU 7E8 code

 

[RonD]

Something is wrong

16k ohms is about 100deg temp for Coolant

Chart is here: https://ww2-secure.justanswer.com/uploads/djenn434/2009-12-24_224727_ect_0000.jpg

Not sure how it showed 9.8volts?
Yellow wire disconnected test?

Sensors use a Signal Return "ground" and the a signal wire back to PCM
5 Volts is the reference voltage to compare to the isolated ground
So the sensor data can't be effected by vehicle voltage or vehicle ground
They are in-effect isolated from rest of the engine systems

P0511 is IAC Valve circuit issue, meaning IAC Valve is not responding to PCM voltage control
IAC valve gets battery voltage with key on, on the Grey wire, test that voltage, should be exactly the same as battery voltage with key on
The grey/orange wire at the IAC Valve is the ground that is control by the PCM, pulsing the ground is the same as lowering the voltage on the positive side, that's the control
On start up the PCM should give IAC valve full ground so it opens all the way, that's why all fuel injected engines should REV on start up, IAC Valve is open all the way
Then when RPMs are above 400 PCM starts to pulse the ground and IAC valve starts to close and RPMs start to drop until "target idle" is set
IAC Valve/PCM setup is accurate within +/-4rpm, so very accurate system

 

[Garyww2]

Ok new headspace, let it rest for a bit and had a few beers!

I let the truck sit overnight. Measured the resistance; 70K something ohms (it went down to +3 last night so makes sence), getting 4.9 (+/- .1v) volts to the sensor (havent a clue how I got the 9.8...) Checked the IAC connector; 11.7 volts read there.

Ran it up; at highway speeds the coolant capped at 195F. Checked the sensor once I got back and after trying to take off the connector it was reading 3K ohms, and 4.9V to the sensor (192F according to the scanner). From my very much uneducated guess I would say the coolant temprature sensor is safe.

I also got the exact RPMs for my issue; after recording it, it will drop to 1230 (going 109 km/hr, then climb to almost 1600 (1550) and then slowly start to go down in RPMs until it hits 1000 (60 km/hr) to which point it stays there until the truck has come to a complete stop (then goes down to 750). And I always wondered why it would rev upon startup, never thought much of it.

 

[RonD]

Good testing on the ECT, yes looks good

Manual transmission computers are set to hold RPMs high for shifting when speed is above 5mph, its an emissions thing, idling engines pollute more than engines above 1,000RPM

But it should only hold the higher RPMs for about 5 seconds when clutch pedal is down, so if you hold down clutch pedal RPMs should drop to about 1,000 at any speed above 5MPH
But Emissions settings could have changed(happens yearly, lol), there may be higher target idles at higher speeds
You can check with local Ford Dealer to see if there is a software update for your VIN that corrects higher RPM idle at speed

But it is normal for idle to stay high, 1,000rpm, until you are stopped, well at least under 5MPH

 

[Garyww2]

The 1000 rpms makes sence, it's been like that since I got it at 98K. What worries me is the drop to 1200, then up to 1500, and then slowly leaning down to 1000 (Clutch is out for the entire thing, I rarely ride the clutch any more than I have to). I have to stop by the dealer tomorrow to pick up the PCV valve, so I will ask that as well. Fingers crossed maybe its just the PCV!

 

[Garyww2]

An update!

Replaced the PCV valve after a rather expensive trip to the dealership. This solved the problem. Kinda.

Rather than such a dramatic drop, it is much more slower. Drops to 1300 and then climbs slowly back to 15, sometimes 1600 rpms.

Also replaced the TPS this time, this also seemed to somehow have an effect, albeit marginal.

Rechecked the IAC valve. With the new one out of gear and both riding the clutch and laying off the clutch it will stay at around 1800 rpms until it is stopped! Swap out with the old one and it goes back to its old self; dropping to 1300, then back to 1500, then slowing down to 1000. All I can say is WTF.