Throttle plates seating OK? Using needle nose vice grips squeeze close the air coming from/into the plenum from the IACV and Air Regulators. Air leaks around plenum gasket? Injector O rings sealing tight? Check all of the fittings on plenum. Have you deleted the water hoses w/o plugging ports? Loose or missing caps on ports? Keep checking listening for air leak / hissing / etc.