My 1998 Ranger, very basic, forest green, peeling paint, 2.3 liter, manual transmission, no cruise, runs great, no warning lights, no check engine light, nothing weird, EXCEPT:
when I come to a stop light or something else for which I want to stop, I normally (1) take my foot off the accelerator pedal, and (2) push in the clutch, (3) coast up to just before the stopping point, (4) push on the brake and (5) stop - like any normal, decent, old fart, driver usually does. Most of the time the engine RPMs decelerate at step (2), when I push in the clutch. Lately, however, after the engine has warmed up, the RPMs aren't coming down until after step (5) - after the vehicle stops. The RPMs remain constant at the speed when I pushed in the clutch. So, if the engine was revving at 2500 when I hit the clutch, it stays there until the vehicle stops and then the RPMs rapidly decelerate down to normal idle speed. That's weird - and I haven't a clue why and what to fix. And what's weirder is that it doesn't do it all the time.
I'm new to this forum but after reading some of the threads I think I've come to the right place. I will appreciate any direction you can give me in solving my problem.
Thanks,

 

I have something similar to that, when I am coming to a slow down, if I have the A/C on, I get the high rev until I flip the accelerator, then the high rev goes to normal.

Only happens with the A/C on though !

I can't find out why !

 

Could be a few things

Take off TPS(throttle position sensor) and check that you can turn it freely, its not "hanging up" no spots that its hard to turn
With TPS off spray lube on the throttle rod and bushing, on both ends, and work the throttle manually to make sure it can close easily, also that the SPRING to close it is tight

The throttle plate on a running engine does NOT want to close, there is 20+ inches of vacuum inside the intake trying to suck it open when spring tries to close it
Make sure it feels OK no hanging up near closed throttle position
Also test and lube the throttle cable and cruise cable(if so equipped), these can hold open throttle plate if they are dried out


IAC Valve can stick a bit before it closes
The computer is suppose to hold idle high until speedometer is under 5MPH, this is for better emissions, and in a manual trans it should hold current RPM for 3 to 5 seconds between shifts, for better MPG, but after the 3-5seconds it should hold it just above 1,000RPM not above 1,500RPM
It does all this using the IAC Valve

IAC Valve is just a solenoid with a spring, that operates a valve on its shaft
Computer uses PWM(pulse width modulation) on the Negative wire on the IAC Valve
So IAC Valve gets 12volts with key on and computer varies its voltage using its ground wire, and its a very very accurate setup, +/- 3rpm

Good look here on cleaning Ford IAC Valve: https://www.explorerforum.com/forums...-w-pics.84220/

To test, remove IAC valve, 2 bolts, then turn Key on, engine off, computer opens IAC Valve all the way for starting, so full 12volts
Look inside at the valve and plug in its 2 wire connector, valve should OPEN all the way, but thats only 3/8", so not much
Unplug the wires and the spring will close valve all the way
Repeat as much as you want

The valve only moves 3/8" and that can set idles of 500rpms to 2,500rpms, so even a slight "sticking" can be 1,000rpm difference

If you decide to replace a Ford IAC Valve you can only use Motorcraft or Hitachi brand IAC Valves, the other kinds are Step motors NOT Solenoids, they will work but will be erratic or cause wandering idles

PCV Valve
Should be changed every 3 oil changes or two years, which ever comes first
PCV Valve is a reverse vacuum valve
When vacuum is high, at idle, the weight in the PCV Valve is sucked UP and closes off the air flow into the intake manifold
When throttle is open, vacuum low, the weight drops down opening up the valve allowing more air flow into the intake

If PCV valves weight is sticking open then its letting in too much air causing RPMs to hang higher, until weight moves and closes off the valve

Shaking a PCV valve to test if the weight is moving is fine to do, but................its a cheap part and best to just replace it if its more than 2 years old or if you see oil residue on it, because that's also IN IT

 

My 05 Ranger does that as well (3.0/5-spd) but very intermittently and only when AC is on (seldom)
If it happens without AC, chances are pretty good my fat *** foot is on the accelerator and the brake.

Have a 98 Chev 4x4 (5.7/5-spd) occaisionally does the same thing-----since that is the primary commuter, a quick cleaning of the IAC usually takes care of it for a while.

 

I swapped in a new IAC and the problem has disappeared ... so far. I'll keep all the other wealth of information you gave in mind in case the problem reappears. DK

 

Good stuff

Thanks to the update and the FIX