Both sides of the lower intake have shafts with levers sticking out the back, below and on either side of the throttle body. You can see the levers if you hold a light over the water pump belt and look under the throttlebody. On a 95 they are connected to a vacuum diaphram pot with metal linkages. Later years have cables like on a bicycle connected to a black box lower down. I believe the front lever should be rotated clockwise at idle, in any case the levers should rotate 90 degrees when the engine RPM's are above 4k. It will take 2-3 seconds to move and they should go back when the RPM's drop below 3.5k. Operation should be smooth.
Check when working so you see how they work.
Carry a flashlight and check again when it acts up.
Installation of a new unit (I assume you have the box)requires removal of intake duct, throttle body, EGR valve - unless you have really small hands. You may just want to pull the intakes and clean them since oil fumes from the PCV build up in the intake and make the shafts and butterflies stick.
