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mrbalihai

PO519 Caused by Bad Resonator/Air Intake Duct Connection?

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I got a CEL while taking a long trip yesterday in my 2003 Baja. Nothing seemed out of the ordinary with the way the car was driving, but I decided to drive to nearby Subaru dealer and have them pull the code just in case it was something serious. The CEL went out on my way to the dealership, so I skipped it and just drove the car home w/no incident. This morning, I read the code and it turned out to be a P0519 - IDLE CONTROL SYSTEM MALFUNCTION (FAIL-SAFE). I'd gotten this code about 2 years ago, and when the Baja went into limp mode a couple of times, I had the IACV replaced. No problems since.

 

I did some googling, and came across a suggestion to check the air filter cover to see if it was seated correctly. When I did, I noticed that the connection between the air-intake duct and resonator chamber was not mated up properly, so I snapped it into place. Could this have caused the CEL by disrupting the flow of air into the intake manifold?

Edited by mrbalihai

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No. IIRC that engine doesn't have a MAF sensor, so the ECU doesn't have a way to measure airflow going into the engine.

 

P0519 is an electrical fault. Usually its due to a failing Idle Air control Valve. But can also be caused by a sticky Nuetral position sensor (MT only) or a faulty Throttle position sensor sending erratic readings and "fooling" the ECU into thinking there is a problem.

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I figured it wasn't going to be that simple. It didn't go into limp mode or stall, so something is definitely sending a bad signal to the ECU. I've had both the IACV and TPS replaced within the past 3 years, and find it hard to believe that they'd have gone bad again this soon. Any ideas on how to test the neutral sensor?

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Neutral position sensor only applies to manual trans vehicles. The switch tells the ECU when the trans is in Nuetral. This changes how the ECU sets the idle speed. If the ECU thinks the trans is in Nuetral and you let off the throttle, the ECU tries to set the engine speed back to idle. But If the trans is actually in gear the ECU can't set idle speed and it sets a code.

 

The switch is the rear-most on the transmission case. Unplug and unthread it from the case, push the button in and see if it pops right back out. If its slow to return or if it feels like there is any binding or roughness to the switch replace it.

 

 

If yours is automatic the park/Nuetral range switch functions in similar manner, but is usually not a soirce of this problem without other codes or other issues being present.

 

 

What was the source for the new IAC? Used? Subaru? Aftermarket?

 

Another thought is the throttle bore could be heavily carboned and could be holding the throttle open slightly.

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What was the source for the new IAC? Used? Subaru? Aftermarket?

 

It's Subaru, direct from the dealership. It's been over a year since it was replaced, so it's out of warranty. Haven't had a chance to check the neutral position sensor, but will take a look this weekend.

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