Fix a malfunctioning 1979-93 Mustang TAB & TAD vacuum control valve with replacements from 5.0 Resto. The throttle air bypass valve (TAB) & throttle air diverter valve (TAD) are part of your Foxbody SMOG or Emissions system. They are controlled by the PCM via the TAB & TAD Vacuum Control Valves. Fix yours today and get rid of that annoying check engine light at LatemodelRestoration.com. These parts fit 1988, 1989, 1990, 1991, 1992, and 1993 Fox Body Mustang.