ENGINE MISFIRES, ROUGH IDLE STALLS/DIST. VACUUM DIAP. LEAK

Model and Year: 1985 SPECTRUM

Some of the subject vehicles may exhibit rough idle, stall or misfire symptoms; the misfire condition, when it exists, usually affects #4 spark plug.

These symptoms may be caused by a leaking diaphragm in the distributor vacuum advance unit creating an incorrect ignition timing condition.

New parts have been made available which incorporate diaphragm material providing greater life expectancy. These parts can be obtained from GMSPO by ordering the following part numbers appropriate to the transmission type noted.

1985 Model Year M/T 94328369 - Control Assembly Vacuum

A/T 94328370 - Control Assembly Vacuum

Corrective action for vehicles exhibiting any of the above conditions is as follows:

Following service manual procedures, carry out the "Inspection of Vacuum Advance Unit" by applying 400 mm Hg. to unit and checking for correct operation.

If this check indicates a leak at the diaphragm, the vacuum advance unit should be replaced using the appropriate part previously listed.

If the check does not indicate a diaphragm leak, follow other diagnostic procedures described in the service manual.

Labor Operation Number: J3400

Labor Time : .5 Hours

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.