FUEL CONTROL SEC. PAGE 4-43 CONTROLLED IDLE SPEED CHART

MODELS: ALL 1990 LIGHT DUTY TRUCKS W/CPC ENGINES

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 90-6C-49(A) DATED MAY, 1990 TO CORRECT ELEVATION SPECIFICATIONS FOR 4.3L AND V8 ENGINES ALL COPIES OF 90-6C-49(A) SHOULD BE DISCARDED.

This bulletin updates the chart shown on Page 4-43 in the Fuel Control Section of the 1990 Fuel and Emissions Service Manual X9036. This infor- mation is for all 1990 light-duty trucks with gas engines.

1990 CONTROLLED IDLE SPEED

ENGINE TRANS GEAR IDLE SPEED IAC COUNTS* OPEN/CLOSED (D/N) (RPM) LOOP** Manual N 950 (S Truck) 5-20 Closed 2.5L Automatic D 800 (S Truck) 15-40 Closed 750 (M Van) 2.8L Manual N 800 5-20 Open Manual N 550 2-20 Closed Automatic D 537 10-25 Closed 4.3L (under 8500 GVW) Automatic(1) D 500 5-30 Closed Manual(1) N 600 5-30 Closed Automatic(2) D 588 10-25 Closed 4.3L (over 8500 GVW) Manual N 650 12-30 Closed Automatic D 650 20-35 Closed Manual N 600 5-30 Open 5.0L Automatic D 500 5-30 Closed Automatic(3) D 500 5-30 Closed 5.7L (under 8500 GVW) Manual N 600 5-30 Open Automatic D 525 5-30 Closed Manual N 650 5-30 Open 5.7L (over 8500 GVW) Manual(4) N 650 5-30 Closed*** Automatic D 550 5-30 Closed Manual N 750 5-30 Open 7.4L (above 8500 GVW) Automatic D 750 5-30 Open

*Add 2 counts for engines with less than 500 miles. Add 2 counts for every 1000 ft. above sea level (4.3L & V8). Add 1 count for every 1000 ft. above sea level (2.5L & 2.8L).

**Let engine idle until proper fuel control status (open/closed loop) is reached.

***Switches to open loop after 3 minutes.

(1) 4.3L S/T series.

(2) 4.3L High-Output M/L-van series.

(3) 3-Speed Automatic in a C10 pickup with Federal emissions and no A.I.R. system

(4) G-Van or Suburban with a single catalytic converter.

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.