What causes a surging idle speed on a Honda or Acura? Here, we’re addressing that complaint and what to look for when you run into this symptom. Honda has a unique programmed response to excessive idle speed, resulting in the distinctive Honda idle ‘surge’. Don’t be a parts changer and replace the IAC motor!

Engine Performance Diagnostics chapter 20

symptoms 50

  • surging idle when warm

fix 50

  • adjusting the cold fast idle valve

test shown enh 50

  • how to scope test a fuel injector
  • understanding how Honda/Acura controls excessive idle speed
  • how to measure duty cycle on a computer controlled solenoid
  • how to test the electrical IAC solenoid
  • understanding common causes of high idle speed conditions
  • understanding the operation of a Honda cold fast idle valve
  • how to determine if the cold fast idle valve is operating properly
  • how to test for a malfunctioning cold fast idle valve at the throttle body
  • how to inspect and adjust a Honda cold fast idle valve

Tools used

  • lab scope

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(Chapter 20) Idle Speed Problems and Testing

Related videos:

P0507 Idle Control System (RPM Too High) - vacuum leak - GM:


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


P0506 IAC System RPM below expected (vacuum leak) - Ford:


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


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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.

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. 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!