I've recently had a few issues with my Ranger; I've gotten some very helpful advice and it's greatly appreciated. I know have a remaining issue, which I am putting in it's own thread to help others in the future:

2001 Ranger 2.5L 5 speed. I had problems with a rough idle, and idle surging followed by a near stall. Ron suggested that I replace the coil packs and wires and plugs; I did that - excellent advice, thanks Ron; this cured the idle surging/near stall problem. But I still had issues with a very rough, lopey, idle - as if I were running a hot cam. No vacuum leaks anywhere. I then replaced the MAF sensor, and now she's idling very smoothly and consistently.

The following issue remains, which had been an occasional problem, but it's getting worse, and the prior fixes didn't do anything:

When cruising in 4th or 5th gear, between 1800-2300 rpm, it almost feels like the engine is missing mildly; there's a little stumbling and hesitation. Note that she pulls strongly and cleanly through the rev range to redline. She starts right up; little cranking required; no issue.

The other issue is that when decelerating, the engine will oftentimes pick up rpm's on her own: I might be decelerating to 1,200rpms as I approach an intersection, and lately on occasion she's been revving to 3,500 rpms on her own. Sometimes I punch the accelerator a few times and she normalizes; lately, I punch the accelerator with no effect. This is not an all the time occurrence, but it happens often enough, and it's getting worse.

Any ideas? I'm thinking it's a throttle position sensor, but I don't wanna start throwing money at a problem unnecessarily.

Other question: I do a lot of rural driving; if it is the TPS, is it something that can flat out fail and leave me stranded, or do I have a little drive time until my part comes?

Thanks

 

Clean the IAC Valve, pics here: https://www.explorerforum.com/forums...-w-pics.84220/

2.5l will be at different location but works the same way

The TPS just tells the computer when you want to accelerate instantly(MAF sensor is too slow) or decelerate(shut off injectors), so it can't strand you
The gas pedal and cable still operate the throttle plate manually

Its possible the spring that holds the throttle plate closed is broken or weak, this spring needs to be STRONG to hold throttle closed with 30"+ of vacuum when decelerating, weak or broken spring won't close throttle plate so RPMs don't drop
Just open and close throttle plate engine off, and see if its sticking, gas pedal cable is a long shot, but the lube can dry out causing cable to stick

But IAC valve sticking open is the more likely issue

Long shot is a computer software glitch
On a manual transmission the computer uses the IAC Valve to keep RPMs high when shifting gears, its an emissions thing
But if you hold the clutch in for 5 second the RPMs should drop to about 1,100, when when under 5MPH it will drop again to idle level

Now there have been reports of software causing higher RPMs and then not dropping after 5 seconds or when coasting(above 5MPH) in Neutral, this was fixed by Ford re-flashing computer software, which they charge for, $150+
This was just on the 3.0ls if I recall

 

Thank you for your reply; I had had this issue before years ago. Last year I replaced the IAC valve with a Hitachi unit - who I believe makes them for Motorcraft as well.

When I replaced the coil packs, I cleaned the throttle body, and I also went over the IAC; it looked very clean - almost new. I also inspected the harness to the IAC, and it looked both clean and solid (free from abnormal wear). It could be that I got a bad IAC. I will hit it with an appropriate cleaner to be sure.

I will clean the spring on the throttle body, although again, it looked pretty good when I went over the unit. I didn't measure the weight of the spring when I actuated it on the throttle body, but it had some heft to it.

Again, I appreciate your time, and for educating me.

 

After engine is warmed up unplug the IAC Valve, engine will most likely stall but that's OK, restart and go for a drive, remembering to hold idle with gas pedal if you need to stop, as YOU are the idle control now, lol

Anyway, get up to speed and see if you get the hanging or high RPMs like before
If not throttle plate and spring are OK, and its looking more like computer or IAC Valve issue
If it still happens then not the IAC Valve or computer

Check engine light(CEL) will come on when IAC Valve is unplugged, it will go off after its plugged back in, no need to clear it

Yes, Motorcraft or Hitachi are the only true IAC solenoids, other brands are stepper/solenoids so can act up in Fords

 

Thank you for your time, and for educating me.

Since I plan on taking a reasonably long road trip in the middle of the week, would a defective IAC also cause the engine to miss mildly, along with mild stumbling and hesitation, while cruising between 1800-2300 rpms?

 

No, those wouldn't be symptoms of IAC issue

Clean MAF sensor before the trip

Put a can of Seafoam or similar injector cleaner in the gas tank before the trip

Gasoline engines run on an Air/Fuel ratio of 14.7 to 1, what many forget, or didn't know, is that this is a WEIGHT RATIO, not volume
14.7 pounds of air is mixed with 1 pound of gasoline to get this ratio
14.7 grams of air to 1 gram of gasoline
Weight ratio not volume
This is why fuel injectors are rated in Pounds per hour, i.e. your Ranger injector can flow up to 14 pounds of fuel per hour

The computer already knows its running a 2.5 LITER engine, so it knows EXACTLY how many LITERS of air are coming in at ANY RPM, its just Math
Computer also knows a US gallon of gasoline weighs 6 Pounds(imperial gallon 7 pounds), gasoline's weight doesn't change that much warm or cold, a little but not much

Computer knows the volume of air, i.e. 2.5 liters, but not the WEIGHT of that air, that's what the MAF sensor is for, it WEIGHS the air as it passes by, but only about 10%
Most have seen hot air balloons flying, how?
Hot air is LIGHTER than cooler air, so the warmer air inside the balloon cause it to FLOAT above the cooler air around it, very neat
There is also an Air Temp sensor to help the MAF

But for a gasoline engine this whole warm air cold air thing is a pain, thats why you had to tune carbs for winter and summer temps, if you lived somewhere with big swings in temps

Fuel injection is much easier, computer does all the work, and does it well, if it has the correct information from its sensors

Point of the above rant
In your case you have dual spark plugs, so I would rule out spark as the issue for the slight miss or stumbling at mid-RPMs
That leaves compression or air/fuel
Compression should also cause lack of over all power and hard cold starts, which was never mentioned, 2.5l does have a timing BELT and tensioner may be worn out, but longshot

Air/fuel is whats left
So clean the MAF sensor, and make sure air filter is OK
And clean injectors(seafoam or other cleaner)
If MAF or injectors were dirty enough you would get a Lean code set, but just the stumbling for a "little" dirty

 

I thank you for educating me; I will be saving this for future reference.

The miss/stumble was there prior to doing any work on the truck, and it still remained, even after installing a new MAF and a new air filter. I did run Techtron through the tank a few weeks ago.

I've got 65k on the timing belt and tensioner; 55k on the fuel filter. Could the fuel pump be a little weak - although at this point I am just making ignorant guesses.

 

No, its a good guess, but should also get Lean codes with low fuel pressure, and very noticeable loss of power at higher speed/higher fuel demand

Warmed up engine, unplug the EGR's vacuum hose, and plug the hose with a bolt/screw
Go for a drive to see if stumbling is gone
You will get a CEL and code, which will go away after EGR is hooked back up, but can hang around for a day or so

EGR system is used anytime engine is warmed up and has a load, driving, computer could be adding too much exhaust at mid-RPM, causing the stumble
Could be DPFE pressure sensor reporting incorrect exhaust flow vs a computer issue, even a sticking EGR modulator/solenoid

 

First and foremost, I wanna thank you for hanging in there with me; over the past month, I have had some major driveability issues with my truck, and your advice has been extremely helpful. Thank you.

The lean/miss thing between 1800-2300rpms is a recent phenomenon. I did run Techron a month ago, but I forgot to mention that I also ran three tanks of Marvel Mystery Oil after the Techron, and I used it liberally. So to be on the safe side, last week, I ran yet another tank full of Techron.

Unplugging the vacuum line from the EGR didn't do anything; I dunno if the last tank of Techron did it, or if it was the new IAC valve that I installed. Either way, the issue seems to have been ameliorated - although I say this after having driven it only 20 miles / mixed driving, but I didn't notice anything unusual.

And now, my Ranger purrs smoothly at idle; she's like a new truck. Thanks again for your time.

 

vacuum leak, dirty egr, idle engine control

 

First, THANK YOU for this explanation!

Why only about 10%? Is it just a limitation of the sensor?

Thank you again!!

And glad to hear the OP got the truck running smooth!

 

I had the same issue you describe. My fix was to clean contacts of the IAC and the harness connector. I also pinched them slightly to make better contact.