Typical to an intake manifold gasket that is leaking, is an engine misfire, especially with the engine cold. In fact many cars will exhibit absolutely no misfires or idle speed roughness with the engine hot. Some may not even have lean condition trouble codes, in particular with speed density engines (no MAF sensor).

Engine Performance Diagnostics chapter 1 pages 9-14

symptoms 50

  • check engine light (P0300, P0301)
  • misfire especially at low RPMs with the engine cold
  • customer replaced plugs, wires, ignition coil and fuel injectors in an attempt at fixing this problem

fix 50

  • replace intake manifold gasket

test shown enh 50

  • how to perform a cylinder drop test (rpm drop test)
  • how to test for spark with a test light
  • how to use water to locate a vacuum leak

Tools used

  • scan tool
  • squirt bottle

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(Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM

Related videos:

Vacuum leak testing without a smoke machine (a SD Premium video):


Ford F-150 P0171 P0174 Trouble Codes - vacuum leak (water test) :


How to find a vacuum leak with water:


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


Causes of lean condition trouble codes P0171, P0174 - GM 5 3L:


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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!