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Old 02-19-2016
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I am: Sam Derbawka
Join Date: Feb 2016
Location: North Battleford, Sk
Vehicle: 2008 Ford Ranger
Drive Type: 4X4
Engine: 4.0
Posts: 1
Total Props: 0
RPMs not dropping during shift

I wonder if anyone could give me some help on this. I have an 08 4.0 4by XLT 5spd manual with 122,102K. I know that in a manual vehicle the engine is designed so that the RPMs come down slow when you depress the clutch so when you grab the next gear and release the clutch the RPMs match and you're not shock loading the drive line pushing the engine back up to ground speed. In my truck it appears this is accomplished via a computer controlled servo and a throttle cable attached to the throttle yolk. When I shift however the engine speed stays the same for a good 30 seconds before it even starts dropping. By the time it does come down I have lost all momentum and have excessively stressed the throw out bearing. So I just shift normally and be gentle releasing the clutch so that it pulls the engine speed down slowly.

I know that in some vehicles if you're not shifting at a high enough RPM it will do this presumably to tell you to shift higher. But my ranger wants me to shift at like 2,700 to 3 grand. I think I should be able to drive a little more gently than that. Is that servo known to fail or is there a sensor issue on the throtttle body maybe? Any help would be greatly appreciated.
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Old 02-19-2016
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I am: Ron Dean
Join Date: Jan 2014
Location: Vancouver, BC
Vehicle: 1994 Ford Ranger
Drive Type: 4x4
Engine: 4.0
Posts: 4,761
Total Props: 88
The Rangers never got Drive By Wire(DBW) throttles like other Ford models did.

So there is no servo that controls throttle plate position, that is done by the throttle cable or cruise control cable.

And it is normal for RPMs to stay up during shifting but only for a few seconds, this is done to lower emissions not driver shifting related.
RPMs will also hold at about 1,000 until speed is below 5mph, again for emissions reasons

You can often feel the gas pedal position under your foot, at higher RPMs, when problem occurs, push in the clutch pedal and lift foot up on the gas pedal, does the pedal come up all the way?
So is the throttle being held open or does the gas pedal come up all the way?

If the throttle is being held open, gas pedal stays down, it could be a few things.
Sticking throttle cable, they can dry out and get sticky inside
Sticking cruise control cable, same thing, cruise doesn't have to be on, cable is always hooked up to throttle

Leaking vacuum into cruise control, holds throttle open, remove cruise cable from throttle linkage and drive it to see if problem is cruise control related.

Weak or broken throttle spring, at higher RPMs the air flow passed throttle plate is high, when you release the gas pedal this spring must be strong enough to close the throttle plate against the flow of air, if it can't then RPMs will hang high.
Remove throttle cable and cruise cable from throttle linkage.
Open and close throttle manually and feel if it may be binding or otherwise sticky.
Start engine
Rev engine manually and release throttle plate, it should snap closed no hanging, snap closed and quick RPM drop.

If gas pedal in first test comes up all the way then throttle plate is closing as it should.
Only RPM control the computer has is the IAC(idle air control) Valve.
It is on the upper intake by throttle and looks like a tube mounted sideways, that is the electric motor part.
This motor is controlled by the computer and opens an air valve that bypasses the throttle plate, basically a controlled vacuum leak.
Computer uses this to set cold idle and warm idle, because this is a fuel injected engine there are no Jets to adjust air/fuel mix, so computer must be in control of idle and an "idle screw" won't work.

You don't mention any problems with idle levels, or codes.
Cold idle should be 1,100 or higher, it is based on engine temp, colder the temp the higher the idle.
Warm idle should be 650 with a manual trans.

After engine is warmed up and idling, unplug IAC Valve's wire connector, RPMs should drop to 500 or engine may even stall, either is good, it means no vacuum leaks.
If idle stays higher than 700 you have a vacuum leak and that can hold RPMs higher.
4.0l is known for PCV Valve hose leaks, at/under the elbows so often unseen.
But you would generally get codes with that leak.

TPS(throttle position sensor) is for driver input to the computer, this is an input sensor only, no computer control, it tells computer what the driver wants to do, accelerate or decelerate.
If there was a problem here you would also get a code, but it also can't hold RPMs up higher, only air flow into the engine can do that.

Last edited by RonD; 02-19-2016 at 10:30 AM.
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