Engine Controls - Erratic Idle and MIL ON
86chevy16NUMBER: 86-B-110
GROUP: 6E - Emission Controls
DATE: August, 1986
SUBJECT: ERRATIC IDLE AND SERVICE MANUAL REVISION
MODELS: 1986 S/T WITH 2.8L TBI ENGINES
Some 1986 S/T Trucks equipped with the 2.8L TBI engine may experience an erratic idle condition or a "Service Engine Soon" light that stays on. This condition may be caused by the Throttle Position Sensor (TPS) supplying incorrect voltages to the Electronic Control Module (ECM). A voltage test of the TPS switch must be made prior to replacement of the TPS using the Service Manual revision included in this bulletin. If this condition is encountered and the testing indicates TPS replacement is necessary, a new TPS, P/N 17111725, has been released and should be used to correct this condition. The replacement procedures for this operation can be found in Section 6E2-C2-15 of the S-15 Service Manual. When performing the TPS voltage check, a revision must be made to the adjustment procedure on page 6E2-C2-15. The revision should read as follows:
With ignition "On", voltage between terminals "A" and "B" should be between 0.420 and 0.450 volts.