No diagrams or pictures here, but, lots of good information.
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Which plenum-intake or. . . .
very carefully
You have to remove the intake plenum air chamber to get to the 3 plugs against the firewall. It requires to buy intake plenum gaskets and go ahead and replace the PCV hose on the back of the plenum. Need to get from the dealer. Gaskets also from dealer.
remove upper intake plenum
Try checking behind the air intake plenum. It should be a round thing.
You have to remove the intake plenum. It just unbolts.
It is 10 Nm or 89 lb-in for Isolator bolt, plenum bolts, and throttle bolt.
The plenum is the intake manifold.
To replace the intake plenum on a 2.5-liter Mercury Mystique, first disconnect the negative battery cable and remove any components obstructing access, such as the air intake and throttle body. Carefully detach the intake plenum by unbolting it from the engine and disconnecting any vacuum hoses, electrical connectors, and sensors. Clean the mating surfaces, install a new gasket, and then position the new plenum, securing it with the bolts. Finally, reattach all previously removed components, reconnect the battery, and start the engine to check for leaks.
The intake plenum on most cars is bolted directly atop the intake manifold. This is where the air goes after passing through the throttle body.
The intake plenum is simply the top of the upper intake manifold, where the throttle body is attached. It is made of black plastic.
The intake manifold runner control (IMRC) on a 1996 Ford Windstar is located on the intake manifold itself, typically on the lower intake plenum. It consists of a series of valves that are controlled by a vacuum actuator. The IMRC is designed to optimize airflow into the engine by adjusting the length of the intake runners based on engine speed and load. To access it, you may need to remove the intake manifold or other components for better visibility and servicing.