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Ranger idle speed

john112deere

caffeine junkie
Staff member
10,807
405
central Vermont
2009 Ranger, 4.0, 5-speed, just over 100k miles.

I have two symptoms- one is vague, hard to explain, and could have a multitude of causes (at the end of this post). The other is a little more clear-cut (maybe). I'm hoping they're connected.

Short version:
From new, the truck has "high-idled" in neutral when moving. I understand this is by design. More recently, it does it...occasionally. Other times, it'll idle down to 700 or so (normal warm idle) when rolling along in neutral.


(I know this is a "feature" may people want to remove from their Rangers, and I even understand why. But I want it to run the way it left the factory.)



No CEL, idle is smooth and steady. It does seem to hunt a bit more when it's in it's "warmup" high idle than it used to (e.g. when the A/C compressor kicks in/out), but you'd only know it from watching the tach.

Last week, it felt like it was going to die coming up to a stop (but it didn't) and generally ran like crap after that. Additionally, if I took it out of gear when I was off the throttle (engine braking), it would drop to (low) idle FAST, not the usual gentle drop of the tach needle I've grown used to. No codes. I replaced the TPS sensor on a whim, and it seemed to improve.

What I've done:
-new TPS
-cleaned MAF
-cleaned IAC




It's also got a bit of a miss/stumble around 2,000 rpm, that seems worse when it's wet and the truck is cold. New TPS did not help this.

This started a while ago, very slight. I replaced plugs and wires (100k- it was time), but wasn't driving the truck much. A few months later, I took it out on a foggy morning, and it was stumbling worse until it warmed up. This "worse" condition remains when it's damp, though sometimes worse than others. Doesn't feel like it's going to stall, but just doesn't feel like it did when it was new.



My thoughts:
-IAC is bad, and cleaning wasn't enough (But it idles pretty well, once it settles into a warm, low idle?)
-if the ECU is getting speed information from a different sensor than the speedometer, maybe it's not aware the truck is rolling. (But I don't think there is another sensor?)



Any wisdom from the techs?

My next diagnostic step will probably be to buy a connector and a phone app that can tap into the computer and give me real-time readouts. Hopefully I'll see something there that gives me a direction.
 

blacksnapon

Moderator
Staff member
Pay attention to engine coolant temps as well. Remember, if its cold, the pcm will up the idle to help it warm up (even if it just "thinks" its cold. That, and IAC motor, vacuum leaks are other good culprits to watch out for.
 

john112deere

caffeine junkie
Staff member
10,807
405
central Vermont
Thanks Vince- am I remembering correctly that the PCM temp gauge on my dash is using a different temp sensor than the PCM?
 

blacksnapon

Moderator
Staff member
Just off the top of my head, there's a possibility that there are 2 sensors, one for the electric fan, and one for engine temp.
 

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