Post on 17-Jan-2016
IDLE SPEED CONTROLIDLE SPEED CONTROL
ENGINE PERFORMANCE
COLUMBIA BASIN COLLEGE
CBC Automotive Department
IDLE SPEED CONTROLIDLE SPEED CONTROL
To comply with federal emissions standards, idle speed control systems are used
Idle speed controlled by electronic moduleEarlier systems, engines idled in open loopIdle systems depend on inputs to PCM
CBC Automotive Department
Throttle Kicker controlled by Throttle Kicker controlled by Vacuum DiaphragmVacuum Diaphragm
Electrically controlled by solenoidOperates during engine warm up, with air
conditioning on and engine overheatingSome act as a dashpot
327C
CBC Automotive Department
Throttle Kicker and Idle Stop Throttle Kicker and Idle Stop SolenoidSolenoid
Electrically controlledVacuum operated
throttle kicker for additional load
Allows curb idle speed to be lower
Controlled by PCMMust be adjusted
327C
CBC Automotive Department
IDLE SPEED CONTROL IDLE SPEED CONTROL MOTOR (ISC)MOTOR (ISC)
PCM controlledReversible gear drive
dc motorPCM reverses
polarityHas idle tracking
switchMust be adjusted325C
CBC Automotive Department
ISC SchematicISC Schematic
CBC Automotive Department
IDLE AIR CONTROL (IAC)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
CBC Automotive Department
Throttle Body IAC LocationThrottle 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
CBC Automotive Department
IAC SCHEMATICIAC SCHEMATIC
Contains two motor windingsCan test with ohmmeter (GM are 40 - 80 ohms)Use IAC Test tool to check operationCan monitor operation with Scanner
508L
CBC Automotive Department
IAC SCOPE PATTERNSIAC SCOPE PATTERNS
Typical patternsCompare patterns to
known good patternsSome IAC’s operate
on 12 volts and others on less voltage
IAC operates with a duty cycle
CBC Automotive Department
ADJUSTING CURB IDLEADJUSTING CURB IDLE(Idle Hardstop or Minimum (Idle Hardstop or Minimum Idle speed)Idle speed)Minimum idle rpm is
factory adjusted Idle must be adjusted
correctlyPassages must be
cleanSome systems, you
must adjust TPS also
502L
CBC Automotive Department
IDLE SPEED ADJUSTMENTIDLE 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)
CBC Automotive Department