Stuttering and fluctuating RPMs?

2008 MAZDA CX-9

150,000 MILES • 6 CYL • 4WD • AUTOMATIC

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Car has no codes or check engine lights. The RPM goes up and down when stopped from 500-1000 and eventually engine stops. Now while driving on highway, it has a stutter. I cleaned the throttle body and MAS sensor. Nothing helped. Today the stutter got really bad

Jun 27, 2023 at 4:38 PM

JACOBANDNICKOLAS

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Hi,

The idle speed issue you described sounds related to the idle air control valve (IAC). The IAC is responsible for maintaining the engine idle speed.

Here is what I recommend. First, check to see if there are any engine vacuum leaks. Check around the intake manifold as well as vacuum hoses.

Here is a link that explains how this is done:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Also, I found a very interesting technical service bulletin that I attached below so you can read it. It deals with the symptoms you mentioned but is limited to specific vehicles made during the production year. Note that it says VIN numbers below a certain number, see if yours is below it.

Take care,

joe

See pics below.

Images (Click to enlarge)

Jun 27, 2023 at 8:59 PM