Intake Manifold Control Shutter Valve(s)
WARNING: This page is about a different car, the 1996 Ford Probe and 1995 Ford Probe. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect vacuum hose from shutter valve vacuum actuator. Using vacuum tester, apply vacuum to actuator. If shutter valve linkage is drawn into actuator, actuator and shutter valve are okay. If linkage does not move, check for stuck shutter valve or ruptured diaphragm in actuator.