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Hey,

A couple of times over the past week my 1998 Subaru Outback has stalled when shifting down gears, when I restart it, the speedo doesn't work and it sounds like it's missing.

I've pulled over and turned the engine off then back on and it fixes itself right away.

I got codes P1507 & P1540.

The P1540 is the speed sensor and I researched that and seems fairly straight forward to replace.

P1507 is Idle Control System Malfunction (Fail Safe). Anyone have any ideas as to what the problem might be for this.

Could the fact that it happened both times when slowly down and shifting down gears give any clues?

Also I haven't got time to fix it just yet, is there any problems with continuing to drive it for a little bit more before fixing it? It hasn't done it for a few days now and it seems to be idling fine and the speedo is working fine.
 

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2001 VDC/SC One of a Kind
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Check the condition of the battery and ground cables. Especially the ground on the intake, passenger side of the throttle body. Check the output of the alternator. Make sure the plugs above the transmission are plugged in tight.

It may just be a weak battery and ground conductance. The two are not related in any way except grounds.

If you need a battery, replace it, drive the car and let us know if it corrects it.
 

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1993 Legacy LSi with still functioning Air Suspension, 1999 Outback 2.5L 5MT lab Rat
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The P1540 code likely set when the vehicle stalls especially if its still moving when it stalls. The P1507 I would look closely at the ground circuit 1st, esp the small ground from the neg Cable to the front of the battery. If that is clean and tight and the vehicle seems to idle at normal speed then more than loo at The Idle Air Control Valve could be malfuntioning. Another place to look at if the Vehicle is a manual Transmission model the Nuetral switch may be the cause, I have seen these stick and falsely indicate nuetral at freeway speeds then the ECM looks to see idle, if it doesn't see idle within a reasonable time its begins to try and adjust idle down, this can cause stalling as you slow from speed.
 

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2001 VDC/SC One of a Kind
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The P1540 code likely set when the vehicle stalls especially if its still moving when it stalls. The P1507 I would look closely at the ground circuit 1st, esp the small ground from the neg Cable to the front of the battery. If that is clean and tight and the vehicle seems to idle at normal speed then more than loo at The Idle Air Control Valve could be malfuntioning. Another place to look at if the Vehicle is a manual Transmission model the Nuetral switch may be the cause, I have seen these stick and falsely indicate nuetral at freeway speeds then the ECM looks to see idle, if it doesn't see idle within a reasonable time its begins to try and adjust idle down, this can cause stalling as you slow from speed.
This is not totally true. The IACV, both O2 sensors and the temperature sensors all share the same ground lug from the harness at the intake manifold.

There are also ground straps running from the engine to the body in several areas of the engine bay, namely the firewall and at the upper transmission torque mount bracket.

If your temperature sensor is not functioning due to a bad ground issue or its failed, the engine will not idle properly, especially if the ECM is getting a high temperature reading from the sensor. The IACV on this year model never goes bad. Subaru is so confident in this valves operation and longevity that the cost is over $400. It is operated by variance in voltage altering the magnetic pull on the pintle to turn the shaft and open or close it for air flow. Most likely, the temperature sensor may be failing, the ECM is trying to shut the car down due to an overtemp condition by closing the IACV and you get a stall.

Check the grounds and battery. If they are good, replace the 2 wire temperature sensor located on the crossover pipe running from head to head. Both temperature sensors are close together. The single wire sensor is for the gauge.

The reason it runs otherwise is because your foot on the accelerator is providing the engine with air. When you let off and the ECM is closing the valve, it dies.
 

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Hey y'all, first post.

I'm having a similar issue - I'm getting a P1507 on a 99 Outback. We had the IACV replaced, and it was good for a year, now we're getting the error again and it did stall. This makes me think that either the IACV was never an issue, but that replacing it required them to do some cleaning, or the replacement has failed, or it's something totally different.... :)

Could the Neutral Safety Switch actually cause a stall if it was faulty?

Cardoc - can you give more detail on where to find the temperature sensor?

Thanks!
 
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