The Code 53 (EGR vacuum control) diagnostic chart for 3.0L and 3.8L carbureted engines has been revised in the 1985 chassis service manual.
Please update page 6E1-65 of your Firenza, Calais, Cutlass Ciera and Ninety-Eight Chassis Service Manual, Volume 11 and page 6E1-75 of your Cutlass Supreme, Delta 88, Custom Cruiser and Toronado Chassis Service Manual with the chart on the reverse side.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.