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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12978
Experience:  Have owned a repair shop for 25 yrs.
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my 2003 chevy avalanche has just started stalling out when

Resolved Question:

my 2003 chevy avalanche has just started stalling out when I come to a stop and the vehical is in gear even if I am making a slow turn it may stall could this be a battery or alternator problem?
Submitted: 4 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 4 years ago.

what is the engine size?will it start right back up?does the engine light stay on?if so,can you give me the computer codes?how many miles is on the truck?tell me all you can

thanks

Customer: replied 4 years ago.
v8 5300, yes it will start back up right away. no codes, engine light goes out when started and there are 149,750 miles it just seems to idle very low.
Expert:  Tim's Auto Repair replied 4 years ago.

ok

the problem may be the iac valve..this is located on the side of the throttle body..sometimes you can remove these and clean it with carb cleaner and they will work fine.though you may need a new one..please print

thanks

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Description and Operation

 

Idle Air Control (IAC) Assembly
The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls a portion of the bypass air.

An orifice located between the throttle valves also supplies a constant amount of bypass air. By moving a conical valve known as a pintle (3) in toward the seat, to decrease air flow, or out away from the seat, to increase air flow, a controlled amount of air can be bypassed. If engine speed is too low, more air is bypassed in order to increase RPM. If engine speed is too high; less air is bypassed in order to decrease RPM. The PCM moves the IAC valve in small steps, called counts. These can be measured and displayed with a scan tool, which plugs into the Data Link Connector (DLC) . The PCM calculates the proper position of the IAC valve during idle based upon the battery voltage, the coolant temperature, the engine load, and the engine RPM. If the RPM drops below specification and the throttle valve is closed, the PCM senses a near stall condition and calculates a new valve position in or der to prevent stalling.

 

  • Engine idle speed is a function of total air flow into the engine. Idle speed is based on IAC valve pintle position, crankcase ventilation valve flow, throttle valve opening, bypass orifice airflow, and calibrated vacuum loss through accessories.
  • Controlled idle speed is programmed into the PCM, which determines the correct IAC valve pintle position to maintain the desired idle speed for all engine operating conditions and loads.
  • The minimum idle air rate is set at the factory with a stop screw. This setting allows enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a calibrated number of steps, counts, from the seat, during controlled idle operation.
  • If the IAC valve is disconnected and reconnected with the engine running, the idle speed may be wrong. If this occurs, reset the IAC valve by depressing the accelerator pedal slightly, starting and running the engine for 5 seconds , and then turning the ignition OFF for 10 seconds .
Service and Repair

REMOVAL PROCEDURE


 

  1. Disconnect the Idle Air Control (IAC) valve electrical connector.

 


 

  1. Remove the IAC valve attaching screws (4).
  2. Remove the IAC valve (3).
  3. Remove the IAC valve O-ring seal (2). NOTE: Refer to Handling IAC Valve Notice in Cautions and Notices.
  4. Clean the IAC valve O-ring sealing surface, the pintle valve seat, and the air passage.
    • Clean the IAC valve using GM cleaner P/N(NNN) NNN-NNNNor GM X-66A. Use a shop towel or parts brush to remove heavy deposits.
    • If the air passage has heavy deposits, remove the throttle body for complete cleaning.
    • Shiny spots on the pintle or seat are normal and do not indicate misalignment or a bent pintle shaft.
  1. Inspect the IAC valve O-ring for cuts, cracks, or distortion. Replace the O-ring if the O-ring is damaged.

INSTALLATION PROCEDURE

IMPORTANT: If installing a new IAC valve, be sure to replace the IAC valve with an identical part. The pintle shape of the IAC valve and the diameter of the IAC valve are designed for the specific application.


 

  1. Measure the distance between the tip of the IAC valve pintle and the mounting surface (1). If the distance is more than 28 mm (1.1 in) use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve does not cause damage to the valve.

 


 

  1. Lubricate the IAC valve O-ring (2) with clean engine oil.
  2. Install the IAC valve O-ring (2) on the IAC valve (3).
  3. Install the IAC valve (3).
  4. Apply Loctite 262 to the IAC valve attaching screw threads if necessary. NOTE: Refer to the Fastener Notice in Cautions and Notices.
  5. Instant the IAC valve attaching screws (4). Tighten Tighten the screws to 3 N.m (27 lb in) .

 


 

  1. Connect the IAC valve electrical connector.
  2. Perform the Idle Learn Procedure.
Locations
Idle Speed/Throttle Actuator - Electronic
icon_note_blank.gif Notes Locations View
Idle Learn Procedure

IDLE LEARN PROCEDURE
Anytime the powertrain control module (PCM) or the battery is disconnected, the PCM loses power, or the PCM is reprogrammed, the PCMs learned idle position is lost. The engine idle is unstable when the learned idle position is lost.

AUTOMATIC TRANSMISSION

  1. Turn "OFF" the ignition.
  2. Restore the PCM battery feed.
  3. Turn "OFF" the A/C controls.
  4. Set the parking brake and block the drive wheels.
  5. Start the engine.
  6. Ensure that the engine coolant temperature is more than 80°C (176°F).
  7. Shift the transmission into "Drive".
  8. Allow the engine to idle for 5 minutes.
  9. Shift the transmission into Park.
  10. Allow the engine to idle for 5 minutes.
  11. Turn "OFF" the engine for 30 seconds.

MANUAL TRANSMISSION

  1. Turn "OFF" the ignition.
  2. Restore the PCM battery feed.
  3. Turn "OFF" the A/C controls.
  4. Set the parking brake and block the drive wheels.
  5. Place the transmission in "Neutral".
  6. Start the engine.
  7. Ensure that the engine coolant temperature is more than 80°C (176°F).
  8. Allow the engine to idle for 5 minutes.
  9. Turn "OFF" the engine for 30 seconds.
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12978
Experience: Have owned a repair shop for 25 yrs.
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