FUEL CONTROL SEC. PAGE 4-43 CONTROLLED IDLE SPEED CHART. GMC Truck S15 Pickup

VEHICLES AFFECTED: ALL 1990 LIGHT DUTY TRUCKS

This bulletin updates the chart shown on Page 4-43 in the Fuel Control Section of the 1990 Shop Manual. This information is for all 1990 Light-Duty Trucks with gas engines.

1990 CONTROLLED IDLE SPEED

GEAR IDLE SPEED IAC OPEN/CLOSED ENGINE TRANS (D/N) (RPM) COUNTS* LOOP** ------ ----- ----- ----- ------ ------- 2.5L MAN. N 950(S) 5-20 CLOSED AUTO. D 800(S) 15-40 CLOSED 750(M)

2.8L MAN. N 800 5-20 OPEN

3.1L AUTO. D 650 5-15 CLOSED

4.3L MAN. N 550 2-20 CLOSED (under AUTO. D 537 10-25 CLOSED 8500 AUTO.(1) D 500 5-30 CLOSED GVW) MAN.(1) N 600 5-30 CLOSED AUTO.(2) D 588 10-25 CLOSED

4.3L MAN. N 650 12-30 CLOSED (over AUTO. D 650 20-35 CLOSED 8500 GVW)

5.0L MAN. N 600 5-30 OPEN AUTO. D 500 5-30 CLOSED AUTO.(3) D 500 5-30 CLOSED

5.7L MAN. N 600 5-30 OPEN (under AUTO D 500 5-30 CLOSED 8500 GVW)

5.7L MAN. 650 5-30 OPEN (over MAN.(4) N 650 5-30 CLOSED*** 3500 GVW) AUTO. D 650 5-30 CLOSED

7.4L MAN. N 800 5-30 OPEN (under AUTO. D 750 5-30 OPEN 8500 GVW)

7.4L MAN. N 750 5-30 OPEN (above AUTO. D 750 5-30 OPEN 8500 GVW)

*Add 2 counts for engines with less than 5.00 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.