1994 Mercury Marquis idle unsteady and whistling


Engine Performance problem
1994 Mercury Marquis V8 Front Wheel Drive Automatic 120000 miles

I am trying to diagnose a idling problem on a 1994 Mercury Grand Marquis. The car operates smoothly with no performance issues except at idle. At low rpm there is a whistle / howl from the rear of the engine. My first repair was to replace the Intake Air Control Valve but that didn't stop the noise. A matter of fact it added a second problem, the idle speed now slowly oscilates between 500-1000 rpm every 5 seconds. Still no performance issues.

When I pinch and hold the hose to the EGR valve at the intake manifold, the idle becomes steady and the noise goes away. There is a vacuum on the EGR side of that connection too.

Is there an issue with the EGR valve and its controls o the IAC Valvle and its controls?

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have the same problem?
Thursday, October 14th, 2010 AT 9:15 AM

1 Reply

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You have a severe vacuum leak somewhere. The best way to find this is smoke testing but you can also try using a can of carb cleaner and spray a little in suspect areas and listen for engine change to indicate a leak.

There is a rubber "T" fitting at the far rear of the engine that is a very common source of leaks.

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Thursday, October 14th, 2010 AT 11:29 AM

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