ford ranger high idle problem


smitty2855

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I have a 2008 ford ranger xlt with 2.3 DOHC and 5 speed manual tranny. took throttle body off cleaned it was really dirty on back side, put it back in now have an idle problem when I come to a stop sign it will stay at 2000 rpms for a bit then idle down to normal, I thought it was the IAC valve so replaced it still doing it also noticed today that when slowing down and coming to a stop it will idle at 2000 rpms with clutch pushed in and no foot on the gas pedal until I stop then it will come down to normal but if I am moving it doesn't. cleaned MAF sensor and air cleaner is good. doesn't make since to me. maybe TPS but if it has to relearn then it must take a while. throttle linkage looks ok. also is this supposed to have a high idle when cold as like the older cars did with automatic chokes. just a side note been working around cars all my life just not the more modern ones. any ideas will help thanks in advance.
 


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RonD

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Welcome to the forum :)

Maybe you didn't notice it before, but................

Since the late 1990's manual transmission vehicles would maintain a high idle until speedometer was under 5MPH.
This is to reduce emissions, an idling engine is a big polluter.

2,000rpm does sound a bit high though, 1,500 would be better.

After engine is warmed up and idling, unplug the 2 wires on the IAC Valve, it will close and RPMs should drop to about 500 or engine may even stall, either is GOOD, it means no vacuum leaks.
If idle stays high then you do have a vacuum leak, and you will need to track that down.

Since you worked on throttle body I would start there, check hoses and gaskets

There is an Anti-diesel screw on the throttle linkage, looks like an "idle screw" but fuel injection can't use an idle screw.
If this got moved then it could be holding throttle plate open too far
Easy to reset, same test as above, warm engine, IAC Valve unplugged, turn screw until RPMs are at 500, engine barely running
Plug IAC Valve back in and idle should go up to your normal warm engine RPMs, anti-diesel screw is set

Just a heads up, this screw can also be used to set minimum voltage for TPS(throttle position sensor), TPS should read under 1volt, .69-.99v, when throttle is closed, TPS has slotted holes so can be adjusted for this, but a 3rd party TPS might not get there, so this screw can be used to lower its minimum voltage to under 1volt

Another heads up
When you change a sensor or control(IAC is a control) you should clear KAM Memory so computer will relearn the parameters of the new part, it will do this on its own over time, but clearing KAM causes it to do it right away.
KAM = Keep Alive Memory, like inside the radio there is a KAM for radio presets and the clock

Unhook either battery cable for 5 minutes, that will clear the engine computers KAM and of course radios KAM, lol.

Idle may wander a bit after clearing the KAM, computer is relearning IAC Valve positions and other learned parameters
 
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pjtoledo

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my 2005 has done the same thing. probably 4 or 5 times over the years. on one of those it lasted for a couple days. went away on its own and runs fine for many months.
it currently has 344,020 miles on it.
 


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