I have a 2008 Ranger 3.0 4x4 that about 3/4 of the time when I drive it the engine revs up pretty fast and wont idle back down. When stopping I have to hold the brake pretty hard to stop it. The only way to get it to idle normal is to shut it down and restart. What could cause this? Thanks...Bob

 

have you pulled codes yet? any of the parts stores will do it for free

 

Welcome to the forum


Automatic trans I assume

First thing is to see if you might have a vacuum leak

On the upper intake by the throttle there will be the IAC(idle air control) Valve it looks like a can on its side and will have 2 wires connected
IAC Valve is what the computer uses to set the idle, it is just a sliding valve that lets more or less air in, bypassing the throttle plate, to set RPMs at idle.

After engine is warmed up and idling, unplug the 2 wire connector on IAC Valve, valve will close all the way and idle should drop down to 500RPMs or engine may even stall, either is good, it means no vacuum leaks and IAC Valve is closing

If idle doesn't change then there is most likely a vacuum leak.
But could be IAC Valve problem, just 2 bolts and you can remove and clean IAC Valve
And test it by having it off and hooking up it's 2 wires
turn on key
Plug in IAC valve wires, it should open all the way
Unplug wires and it should close all the way
Repeat as much as you want to make sure it is not sticking anywhere along its slide path

If idle does drop down to 500RPM or less then no leak and IAC valve is OK

Computer keeps idle high until speedometer is below 5MPH, it's an emissions thing
So speedometer must be working, you don't mention its not working but may not think that is related.

Have VIN in hand and stop by Ford Dealer, there may be a software update needed for the computer, a TSB about high idle
You may have to pay for it but better than wasting time(or money) on "non-fixes" if its a computer glitch

 

I have a 02 Ford Ranger and changed the air filter and some rotting foam from a nearby line fell in the filter housing and got sucked into the Idle Air Control Valve (IAC) keeping it from shutting completely. This led to a constant high idle, even when switching gears at highway speeds. The IAC is located right next to the throttle body on the engine and can be simply taken off as there are only 2 bolts and a 2 wire clip. You can open the valve easily using your finger nail and shake out any debris caught in there. I cleaned mine with a bit of brake cleaner and let it dry before putting it back on. Now my truck runs like normal again. Funny how the smallest things can make the biggest difference.