How to test an idle control valve (2-wire solenoid type) using a lab scope. This video is for Automotive Picoscope users, but no matter what type of scope you have, the information contained in this video will help. Even if you do not have a scope, you can still follow this material and measure IAC duty cycle with your digital multimeter.

Engine Performance Diagnostics chapter 20 pages 21-26

symptoms 50

  • stalling problems
  • start stall
  • low idle speed
  • car runs normal if your foot is on the gas pedal
  • check engine light with idle speed control error fault codes

fix 50

  • how to test an idle air control valve (solenoid type)
  • how to determine power and ground side switching
  • how to measure duty cycle

test shown enh 50

  • how to test for spark
  • how to test fuel pressure on a system with no pressure regulator
  • how to test a fuel pump driver module on a Ford
  • how to test fuel pump power and ground
  • how to test an inertia switch on a Ford
  • how to test the PCM control signals to the FPDM

Tools used

  • Picoscope (automotive 4 channel kit)

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(Chapter 20) Idle Speed Problems and Testing

Related videos:

Ford Idle Air Control (IAC) valve test (how to adjust minimum idle speed) :


Ford idle air control valve (IAC) test - stalling problems:


Causes of low compression, no start from a stuck closed IAC (part 1) - Toyota/Lexus :


Causes of low compression, no start from a stuck closed IAC (part 2) - Toyota/Lexus :


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

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