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

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Published on Apr 20, 2012

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
https://www.youtube.com/playlist?list...

Related videos
- Causes of low compression, no start from a stuck closed IAC (part 2) - Toyota/Lexus https://youtu.be/9c1YSic7ejs
- Broken timing chain with good spark - GM 2.2 (part 1)
https://youtu.be/noldvC_3qY0
- Broken timing chain with good spark - GM 2.2 (part 2)
https://youtu.be/2SmmLXGpa58
- Honda Civic 1.7 (start, run, stall case study)
https://youtu.be/i6x31RU1S_I

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 right here on YouTube. 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!

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