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
   • (Chapter 1) Misfire ID, Compression T...  

Related videos
Causes of low compression, no start from a stuck closed IAC (part 2) - Toyota/Lexus    • Causes of low compression, no start f...  
Broken timing chain with good spark - GM 2.2 (part 1)
   • How to identify a broken timing chain...  
Broken timing chain with good spark - GM 2.2 (part 2)
   • How to identify a broken timing chain...  
Honda Civic 1.7 (start, run, stall case study)
   • Honda Civic 1.7L starts, runs, stalls...  

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.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https://www.scannerdanner.com/join-sc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!

Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.