If you have 80's P30 with air pump canister ,two if its set up for California EPA check the canister(top pops off) for filter over a wire mesh center, replace with new filter from GM or a quick temp fix,use a piece of air condition foam filter on both sides of wire mesh frame. Mine started to make a loud noise like engine was surging. A check of filter found foam part crumbling and mostly gone. Access is inside cabin,in carpet under pass. side carpet(6x6" square cut in carpet and plywood flooring. This may be why pump failed or did it just get ola(17 years), drivers side pump appears ok but check it often. JKB

While you're messing with the filters, I'd suggest fabricateing clamps to hold down the caps. My SOB also has the twin AP arrangement, and I got considerable drumming from the caps, and the snap-fit didn't secure the caps. They popped up and down on each stroke of the pump, and created a lot of noise.

I made my clamps from threaded rod bent into a "U" and an aluminum strip (with a piece of weatherstrip foam on the contact side) across the top, secured with wing nuts and lock washers. A piece of rubber tubing at the bottom of the "U" keeps the threads from cutting into the casing.