The old design plenums have shaft bushings that wear out, letting the shaft and butterflies flutter, which eventually breaks the screws on the b'flies and off they go to smash into the valves and pistons, plus the air leak at the bushings leans out the mixture, causing bad idle and emissions problems.

You have three options. One, disco the butterfly actuator and wire it open. Two, repair the bushings, and three, buy a new lower plenum for several hundred bucks.

One loses a tad of power and mileage and is dead cheap. Two fixes the problem, and is tricky and delicate to do. Three fixes the problem and is simpler to install/fix, and has improved bushing material. Depending on the bbushing material used, two may be a superior fix. I'd think the best material would be phosphor bronze. I think the original bushings are plastic. THere are better plastics, too, but p-bronze is self lubricating and hard.

There is a fourth repair, in which you just remove the shaft and b'flies and plug the two end holes, fairly cheap and very sloppy.