1989 Ford F-250 Idle Air Control Sensor

Tiny
JAM39
  • MEMBER
  • 1989 FORD F-250
  • V8
  • 2WD
  • AUTOMATIC
  • 135,000 MILES
Why do I not have 10.5 volts from PCM to IAC sensor.
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Monday, March 15th, 2010 AT 2:49 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
What's the symptom?

It's not a sensor; it's an output. The higher the voltage, the further it opens to allow in more air to control idle speed.

Caradiodoc
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Monday, March 15th, 2010 AT 2:53 PM
Tiny
JAM39
  • MEMBER
Why am I missing voltage to my IAC from the PCM
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Monday, March 15th, 2010 AT 2:56 PM
Tiny
CARADIODOC
  • EXPERT
Sometimes there is not supposed to be voltage to it. The higher the voltage, the higher the Engine Computer is trying to raise engine speed.

What is the symptom? Does the engine stall? Will it run if you hold the gas pedal down a little? Is the engine running too fast at idle? Need to know what the symptom is, otherwise, the system could be working normally.

Caradiodoc
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Monday, March 15th, 2010 AT 4:20 PM
Tiny
JAM39
  • MEMBER
I recently cleaned to upper intake including the IAC
control, and before cleaning the idle was a much
higher RPM and decreased when engine reached
normal op temp.
I read in a HAYNES repair manual that the IAC should
have 10.5 volts with key on engine off.
I hope this helps.
Jim
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Monday, March 15th, 2010 AT 4:39 PM
Tiny
CARADIODOC
  • EXPERT
First of all, I messed up. The control wire gets grounded by the Engine Computer. It doesn't apply voltage on the control wire.

I spoke with a Ford expert who said they don't normally check for this voltage. If the system is working properly, the engine will stall when the IAC is unplugged. If stalling does not occur, suspect a vacuum leak.

You might also measure the voltage on the connector when it's unplugged from the IAC unit. If it is there, but not when it's plugged in, look for a corroded spot in the wire, typically a pin in a connector. If the voltage is still missing, measure on that wire at the Engine Computer connector.

Caradiodoc
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Monday, March 15th, 2010 AT 5:58 PM
Tiny
JAM39
  • MEMBER
Thanks very much for your help.

Jim
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Monday, March 15th, 2010 AT 6:36 PM

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