1999 Chevy Silverado IAC motor

Tiny
CHEVY166
  • MEMBER
  • 1999 CHEVROLET SILVERADO
1999 Chevy Silverado Two Wheel Drive Automatic 63000 miles

What tells the IAC motor what to do?
Do you
have the same problem?
Yes
No
Saturday, July 18th, 2009 AT 8:29 PM

4 Replies

Tiny
RASMATAZ
  • MEMBER


http://www.2carpros.com/forum/automotive_pictures/12900_iac_idle_air_control_motor_1.jpg



How Does an Idle Air Control Valve Work? (IAC)
An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The car computer or ECM (electronic control module) receives information from various sensors and will output signals to adjust the IAC motor in or out to adjust engine idle speed by controlling engine idle air. An IAC motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the IAC control motor to react slowly, either failure will cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak IAC motor. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed.

Idle Air Control Valve (appearance will vary)

Common Problems

An IAC motor is highly susceptible to carbon and coking build up; if an IAC goes too long without cleaning it can cause stalling and poor idle quality. Some cars are designed with a large vacuum transfer hose that connects the intake manifold to the IAC (idle air control) motor. If a broken or dilapidated these vacuum lines can cause the engine to lose vacuum which will allow the engine to run rough and die. Inspect all engine and accessory vacuum lines to look for missing, torn or dilapidated lines and replace as needed. Any car that is designed with a magnetic non-motor operated IAC like Lexus is subject to carbon and should be cleaned about every 40,000 miles to avoid stalling.

Basic Maintenance

To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed
Was this
answer
helpful?
Yes
No
Saturday, July 18th, 2009 AT 8:38 PM
Tiny
CHEVY166
  • MEMBER
IAC motor seams to be working correctly. It's new so I moved the plungger in to less than 1 1/8. Start the truck idles fine put it in drive as part of the procedure and it runs a few minutes and then goes back to the way it was before I changed out the motor. Mass flow is good speed idle sensor is good. What causes the change?
Was this
answer
helpful?
Yes
No
Saturday, July 18th, 2009 AT 8:49 PM
Tiny
RASMATAZ
  • MEMBER
Test the MAF and TPS sensors.
Was this
answer
helpful?
Yes
No
Saturday, July 18th, 2009 AT 9:04 PM
Tiny
CHEVY166
  • MEMBER
Both are ok
Was this
answer
helpful?
Yes
No
Saturday, July 18th, 2009 AT 9:19 PM

Please login or register to post a reply.

Recommended Guides