WARNING: This page is about a different car, the 1995 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
Code P099 may be inadvertently induced by technician using cruise servo to bump up throttle.
Fig 1: Code P099 Schematic, Cruise Servo Applied Not In Cruise
Courtesy of GENERAL MOTORS CORP.
Fig 2: Code P099 Diag. Flow Chart, Cruise Servo Applied Not In Cruise