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IDLE SPEED CONTROL IDLE SPEED CONTROL  To comply with federal emissions standards idle speed control systems are used  Idle speed controlled by electronic module  Earlier systems eng

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IDLE SPEED CONTROL IDLE SPEED CONTROL  To comply with federal emissions standards idle speed control systems are used  Idle speed controlled by electronic module  Earlier systems eng Powered By Docstoc
					IDLE SPEED CONTROL
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
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

                                             327C
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
       327C      Must be adjusted
IDLE SPEED CONTROL
MOTOR (ISC)
            PCM controlled
            Reversible gear drive
             dc motor
            PCM reverses
             polarity
            Has idle tracking
             switch
   325C     Must be adjusted
ISC Schematic
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
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
                                      508L

IAC SCHEMATIC




   Contains two motor windings
   Can test with ohmmeter (GM are 40 - 80 ohms)
   Use IAC Test tool to check operation
   Can monitor operation with Scanner
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
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

                          502L
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)
END

				
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posted:8/24/2011
language:English
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