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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12805
Experience:  Have owned a repair shop for 25 yrs.
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1998 Chevy Malibu: I take my foot off the gas, it dies

Customer Question

My 1998 Chevy Malibu starts. If I take my foot off the gas, it dies. Foot on gas, it's good. Replaced the TPS, Fuel Filter, Battery and battery cables/connections good, replaces water pump. Got a V6. No check engine light is on. Plugged in code tester and got no error codes. What gives???
Submitted: 3 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 3 years ago.

hi

this sounds like you may have a bad iac [idle air control valve]somtimes you can remove and clean these with carb cleaner and they will work fine,,thoough you may need a new one

thanks

 

Description and Operation

The purpose of the Idle Air Control (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 bypass air around the throttle plate. By moving a conical valve, known as a pintle, in (to decrease air flow) or out (to increase air flow), a controlled amount of air can move around the throttle plate. If RPM is too low, the PCM will retract the AC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.

The IAC pintle moves in small steps called counts.

During idle, the proper position of the IAC pintle is calculated by the PCM based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74 volts ), the PCM senses a near stall condition. The PCM will then calculate a new AC pintle position to prevent stalls.

If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.

The IAC resets when the key is cycled ON then OFF. When servicing the IAC, it should only be disconnected or connected with the ignition OFF in order to keep from having to reset the IAC.

The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is open fully, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. DTC P0507 may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with possible hard starting and a rich air/fuel ratio. DTC P0506 may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.

Service and Repair

REMOVAL PROCEDURE


 

  1. Turn OFF the ignition.
  2. Disconnect the electrical connector from the Idle Air Control (IAC) valve.

 


 

  1. Remove the two AC valve attaching screws.

 


 

  1. Remove the idle air control valve.

 


 

  1. Remove the idle air control valve O-ring.

INSTALLATION PROCEDURE

NOTE: The AC valve may be damaged if installed with the cone (pintle) extended more than 28 mm (1-1/8 in) . Measure the distance that the valve is extended before installing a new valve. The distance from the idle air control valve motor housing to the end of the idle air control valve pintle should be less than 28 mm (1-1/8 in) . Manually compressing the pintle until the extension is less than 28 mm (1-1/8 in).


 

  1. Install the new idle air control O-ring.

 


 

  1. Install the idle air control valve into the intake manifold.

 

  1. Install the two idle air control valve attaching screws. Tighten Tighten the screws to 3.0 N.m (27 lb in) .

 


 

  1. Connect the idle air control valve electrical connector.
  2. The PCM will reset the idle air control valve whenever the ignition is turned ON then OFF. Turn the ignition ON then OFF.
  3. Start the engine and allow the engine to reach operating temperature.

 

Locations View (3100 LG8)

Idle Air Control (IAC)
Locations
icon_note_blank.gif

Customer: replied 3 years ago.
I appreciate the advice. I'm going to replace it. Just checked the price and it's not bad at all. If it works, then I will gladly accept your answer and leave positive feedback. Please give me time though. May take a few days. Thanks!
Expert:  Tim's Auto Repair replied 3 years ago.

that will be fine....before you buy 1..you do need to check for vacuum leaks and also you may want to try cleaning it

thanks

Customer: replied 3 years ago.
Well, I pulled the idle air control valve out and it was dirty. A lot of carbon build up. So I cleaned it real good with carb cleaner. Put it back in and had no issues all day! Then, this morning, I had the issue again for about the first hour of driving around, then it was fine again. I believe this is the issue because for two weeks prior to yesterday, it was happening literally everytime I drove the car. Was it not cleaned enough? Should I replace it? I'm going to replace the air filter as well, could that be contributiing to the problem? Thanks!
Expert:  Tim's Auto Repair replied 3 years ago.

hi

sense the cleaning did fix it somewhat,yes,install a new one,,i don't think the air filter is the problem,but if it is dirty,do replace it

thanks

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