1985 Corvette: Service Bulletin: Minimum Idle Speed Revision
Model Year: 1985 Corvettes with Automatic Transmission
Subject: Minimum Idle Speed Revision
Source: Chevrolet Dealer Service Bulletin
Bulletin Number: 85-91, Section 6
Date: May, 1985
TO: ALL CHEVROLET DEALERS
Some 1985 Corvettes equipped with the L98 5.7L engine and automatic transmission may not be able to maintain the minimum idle speed.
Below minimum idle speed is most likely to occur when the vehicle is traveling less than 5 mph and the T.P.S. reading is equal to or less than 2%. When these conditions are met, the I.A.C. valve will try to control the engine speed to the idle command speed and may "learn" its self to the zero position. When the I.A.C. valve is seated, the only air entering the engine is the air passing around the throttle plates. This air is referred to as "minimum air" and is factory set to allow an engine speed of 400 RPM.
If the throttle is closed while the I.A.C. valve is seated, the engine may stop running, since the only air entering the engine is that allowed by the minimum air setting.
This condition can be repaired by resetting the minimum air rate to 500 RPM. The procedures to be followed for this repair are detailed in Section 6E3-91 (minimum air rate adjustment) of the 1985 Corvette Shop Manual.