OBD II code for Idle Control System malfunction

Tiny
ROBERT CATES
  • MEMBER
  • 1996 SUBARU LEGACY
  • 2.2L
  • 4 CYL
  • AWD
  • AUTOMATIC
  • 240,000 MILES
Car was fine one day then the next would not run. Will start but soon stalls out. CEL came on with a P0505. Have checked all vacuum lines and can not find a leak. I have noticed that the IAC valve continues to be energized for a while after the engine is turned off. I was told by a parts dealer this means that the motor has an internal short and needs to be replaced. As I know he would love to sell me a $350 part I thought I would get a second opinion. I have pulled and cleaned the IAC. Is there a simple test to determine if the motor is bad? There are three prongs on the wiring connector. Could a fault in the ECU cause the IAC to continue to receive power? I would think this could also be a symptom of weak fuel pressure, but would that throw a code?
Thanks.
Tuesday, April 22nd, 2014 AT 2:56 AM

3 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
I don't know how you concluded that the IAC is active after the key is turned off but it should not be receiving any power supply with the key off. The main relay supplies that.
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Tuesday, April 22nd, 2014 AT 3:10 AM
Tiny
ROBERT CATES
  • MEMBER
  • 2 POSTS
I can hear it buzzing. When I pull the wiring harness off it stops. This is true even with the IAC removed from the manifold. Turning the key to on, then back off, you can see that the valve is torqued, and hear it buzzing, until you remove the harness.
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Tuesday, April 22nd, 2014 AT 3:35 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
It has to be receiving power when it shouldn't. I would check out the main relay and see if it is sticking on.
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Tuesday, April 22nd, 2014 AT 4:17 AM

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