Do It Yourself
Intake Manifold Vacuum Test
Intake Manifold Vacuum Test:
Taking a vacuum reading of the intake manifold can help you diagnose engine problems and specific problems relating to the cylinder head. All that is required is vacuum gauge which can be purchased for under $20 at most auto part and hardware stores.
The procedure is basically the same for all Probes. Begin by starting the engine and allowing it to reach normal operating temperature. Once normal operating temperature is achieved, check to make sure that the idle is within specification:
2.2L 4-Cylinder - 725-775rpm
2.2L 4-Cylinder Turbocharged - 725-775rpm
3.0L V6 - 725-775rpm
2.0L 4-Cylinder - 650-750rpm
2.5L V6 - 600-700rpm
If the idle speed is not within specification, the intake manifold vacuum test can still be performed, but results will be less accurate.
Turn the engine off. Remove a vacuum line from the intake manifold and connect the vacuum gauge directly to the manifold, assuring that the connection is tight and no leaks are present. Make sure you plug up the vacuum line that was removed. Restart the engine and allow it to idle. The vacuum gauge should read between 15 and 22 inches on first generation Probes and between 17.7 and 22 inches on second generation Probes depending on the engine's condition and the altitude at which the test is performed. Subtract 1 inch from the reading for every 1,000 feet of elevation above sea level.
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