1992 GMC Pickup C3500, 4D Pickup, 5.7 K, StandardFACTORY OEM SERVICE PROCEDURE

Idle Speed & Mixture

NOTE: Idle mixture on fuel injected models is controlled by the Electronic Control Module (ECM) and is not adjustable. Controlled idle speed and IAC count can be checked using scan tester. See CONTROLLED IDLE SPEED & IAC COUNT table.
CONTROLLED IDLE SPEED & IAC COUNT

Application Idle RPM (1) IAC Counts
2.5L TBI "S" Series
Auto. Trans. (2) 800 15-40
Man. Trans. (3) 900 5-20
2.8L TBI "S" Series
Auto. Trans. (2) 800 5-20
3.1L TBI "U" Series
Auto. Trans. (2) 600-700 5-15
3.8L PFI "U" Series
Auto. Trans. (2) 650-750 16-20
4.3L CPI
"L" Series Auto. Trans. (2) 625 5-50
"M", "S" & "T" Series Auto. Trans. (2) 550 5-40
4.3L PFI Turbo "S" & "T" Series
Auto. Trans. (2) (4) 1-50
4.3L TBI
"C" & "K" Series
Auto. Trans. (2)(5) 537 5-30
Auto. Trans. (2)(5) 650 20-35
Man. Trans. (3) 550 2-20
"G" Series
Auto. Trans. (2) 538 5-30
Man. Trans. (3) 650 5-30
"L" Series
Auto. Trans. (2) 625 5-50
Man. Trans. (3) 600 3-30
"M" Series
Auto. Trans. (2) 538 5-30
"P" Series
Auto. Trans. (2) 650 20-35
5.0L TBI "C" & "K" Series
Auto. Trans. (2) 500 5-30
Man. Trans. (3) 600 5-30
5.7L TBI
"C", "G", "K" & "P" Series
Under 8500 GVW
Auto. Trans. (2) 525 5-30
Man. Trans. (3) 600 5-30
Over 8500 GVW
Auto. Trans. (2) 550 5-30
Man. Trans. (3) 600 5-30
7.4L TBI
"C", "G", "K" & "P" Series
Auto. Trans. (2) 750 5-30
Man. Trans. (3) 800 5-30
(1) Add 2 counts for engines with less than 500 miles. On 4.3L V8 engines, add 2 counts for every 1000 ft. above sea level. On 2.5L & 2.8L engines, add 1 count for every 1000 ft. above sea level.
(2) Automatic transmission in Drive.
(3) Manual transmission in Neutral.
(4) Set to +/-50 RPM from desired idle speed in Drive.
(5) Calibration identification not given by manufacturer. IAC count and actual RPM should correspond to one of these calibrations.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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