1. ENGINE PERFORMANCE COLUMBIA BASIN COLLEGE
IDLE SPEED CONTROL
ENGINE PERFORMANCE
COLUMBIA BASIN COLLEGE

2. IDLE SPEED CONTROL
To comply with federal emissions standards, idle speed control systems are used
Idle speed controlled by electronic module
Earlier systems, engines idled in open loop
Idle systems depend on inputs to PCM
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3. Throttle Kicker controlled by Vacuum Diaphragm
Electrically controlled by solenoid
Operates during engine warm up, with air conditioning on and engine overheating
Some act as a dashpot
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327C

4. Throttle Kicker and Idle Stop Solenoid
Electrically controlled
Vacuum operated throttle kicker for additional load
Allows curb idle speed to be lower
Controlled by PCM
Must be adjusted
327C
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5. IDLE SPEED CONTROL MOTOR (ISC)
PCM controlled
Reversible gear drive dc motor
PCM reverses polarity
Has idle tracking switch
Must be adjusted
325C
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6. ISC Schematic
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7. IDLE AIR CONTROL (IAC) Used with Fuel Injection systems
PCM controlled Stepper motor
Diverts air around throttle plate
Do not over extend when replacing
Not adjustable
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8. Throttle Body IAC Location
Screws into throttle body
Must be careful to not over-tighten
Must keep passages clean
Can use Scanner to diagnose idle problems
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9. IAC SCHEMATIC Contains two motor windings
508L
IAC SCHEMATIC
Contains two motor windings
Can test with ohmmeter (GM are ohms)
Use IAC Test tool to check operation
Can monitor operation with Scanner
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10. IAC SCOPE PATTERNS Typical patterns
Compare patterns to known good patterns
Some IAC’s operate on 12 volts and others on less voltage
IAC operates with a duty cycle
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11. ADJUSTING CURB IDLE (Idle Hardstop or Minimum Idle speed)
Minimum idle rpm is factory adjusted
Idle must be adjusted correctly
Passages must be clean
Some systems, you must adjust TPS also
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502L

12. IDLE SPEED ADJUSTMENT
Must shut off idle air to adjust minimum idle speed
Use idle plug on TBI units
Other systems, you just turn a screw to control air flow (idle rpm)
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13. CBC Automotive Department