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Odd idle behaviour

  #1  
Old 01-04-2019
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Odd idle behaviour

Hey all,

I've got a '97 ranger splash. It's idol is behaving odd and its become somewhat of a problem in the winter.

Over the summer I've noticed whenever I put the clutch in or go to neutral, the idle goes up to around 2000 RPM and stays there for 5 to 10 seconds, then comes back down to around 700. Annoying, but not a problem. I only include this to help potentially diagnose.

When the truck is cold in the winter, it initially starts like one would expect with high idle... But then after a minute the idle drops down and the truck shuts off. Starting it again, it'll constantly oscillate between high idle, then almost stalling. Sometimes it'll catch and go back to high idle again, but then drops again after a few seconds. Sometimes it'll shut off when it drops, but not always. When the truck is eventually warmed up, it stops oscillating... but it still does the high idle as describe above in the summer.

So does anyone have any idea where I could start looking for a potential solution? Is there some sort of faulty regulator?

Thanks so much!
Trevor
 
  #2  
Old 01-04-2019
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On all fuel injected engines they use an air valve to control the idle, on Ford's its called the IAC(idle air control) Valve

It is located near the throttle plate, looks like a can laying on its side

It is a 12volt solenoid with a spring inside, the computer adjusts the voltage to this solenoid to pull it open against the spring pressure trying to hold it closed
This is a very accurate way to set idle, +/- 4RPM usually

But the computer relies on a few things to set a stable idle
First is the engine temperature, ECT(engine coolant temp) sensor is used for that
There are TWO temp devices on your engine
ECT sensor used by the computer, always has 2 wires connected, one will be light green/red stripe
and
ECT SENDER used by dash board temp gauge, these often just have 1 wire connected, red/white wire

ECT sensor is not expensive, so often just easier to replace it to take that off the table as possible problem

IAC valve can be cleaned
Info here: https://www.explorerforum.com/forums...-w-pics.84220/

Vacuum leaks
Easy way to test for vacuum leaks is to warm up the engine, let it idle, then unplug the IAC Valves two wire connector
IAC Valve will close and engine RPMs should drop to 500 or engine may even stall, either is good, it means no leaks

On manual transmissions there is a emissions control software that should hold RPMs high when you are moving and shifting gears, so when clutch pedal is pushed in and speedometer shows above 5MPH the RPMs should hold, not go up, but hold and then if you leave pedal in they will drop after 5-8seconds, but stay at or just above 1,000RPMs
When speed drops under 5MPH then idle should be back to 650-700

This is done using a switch on the clutch pedal's pushrod, safely switch for starting but also tells computer when clutch pedal is down all the way, so when you press clutch pedal down the computer "sees" that and initiates this emissions software that should adjust the IAC Valve to set the higher idle, IF.............you are moving faster that 5MPH
It should not do this if you are stopped
 
  #3  
Old 01-04-2019
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My truck was doing something similar, turned out to be the intake hose. The part between the air filter box and throttle body, it had some cracks in it and even though I wrapped it with duct tape the idle problems never went away until I replaced the intake hose with a new one. Now my truck idles perfectly.
 
  #4  
Old 02-13-2019
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I thought I'd give an update. I replaced the air idle control valve and now its purring like a kitten! That did the trick, and only a 10 minute job. Thanks for all the help!
 
  #5  
Old 02-13-2019
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Good work

Thanks for the update and the FIX
 
  #6  
Old 02-13-2019
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Join Date: Feb 2019
Location: Porterville
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Easy fix

Must be nice good job hoping mine is as easy
 
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