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

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.
In part 2, I will show you how to test and clean the idle air control motor itself.

Engine Performance Diagnostics chapter 1

Symptoms
no start with good spark, injection pulse and fuel pressure
no compression
very high cranking vacuum

Fix
clean stuck closed idle air control valve

Tests shown
what an engine sounds like during cranking with no compression
compression test
cranking vacuum test
cam and crank relationship on a lab scope
how to verify cam timing
in cylinder pressure transducer testing
ignition timing verse cylinder pressure waveform
how to identify a proper timing with a scope

Tools used
Picoscope
vacuum gauge
compression gauge

Playlist
(Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM
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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
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