It is the 3.5" diameter vacuum diaphragm actuator on the driver side rear of the intake plenum. It is mounted to the intake by two bolts on the ******. A 10mm nut and 12mm bolt (long hex section) on the upper end and a 12mm bolt on the lower side. If it is plugged, it will be easy to see. Clean the 1/2" diameter passage with intake cleaner and swabs. If the valve itself is plugged (not likely?), you may need a new valve.
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Scott
1991, 254K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
6 disc CD, Class II hitch, Silver award at SHOklahoma Car Show