In this part 2 video we will focus on testing and cleaning the idle air control motor. This was one of the weirdest causes of a no compression, no start problem that I have ever seen. Someone could have easily condemned the engine itself for this problem. Every other time I have heard an engine crank like this (no compression has a unique sound), it has always been a jumped or broken timing belt or chain. Going into this, I would have never thought a stuck closed idle air control motor could cause this condition. I've seen many sticking IAC motors in the past and with every single one of them, the engine would at least start up and run for a second or two.

Engine Performance Diagnostics chapter 20 pages 25-26

symptoms 50

  • no start
  • start stall
  • will not idle unless the gas pedal is held open

fix 50

  • clean stuck closed IAC valve

test shown enh 50

  • description and operation of the idle air control motor
  • how to test a 3 wire idle air control valve/solenoid
  • how to remove and clean an idle air control valve
  • wiring diagram review of a 3 wire IAC motor
  • how to measure a duty cycle controlled output
  • dangers of T pins

Tools used

  • digital multimeter
  • lab scope (Picoscope)
  • backprobing pins

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(Chapter 20) Idle Speed Problems and Testing

Related videos:

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


How to test an idle air control valve (IAC) using a Picoscope - Ford :


Chapter 20 "Idle Speed Controls" - preview (an SD Premium video) :


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


How to test an Idle Air Control (IAC) valve - Nissan/Infinity:


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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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