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1 hour ago, GeneralDisorder said:

Sounds like an intermittent electrical connection. Being in Alaska I would put my money on corrosion somewhere. Start wiggling wiring connections and harnesses with the engine running and see if you can replicate the issue. Sounds like it's related to the drivetrain shifting when driving at lower speeds and accelerating from a stop, etc since you say it rarely, if ever, does it on the highway. 

Another potential is a dead spot in the TPS. Check it with a scope if you can. 

Don't troubleshoot with the parts cannon. 

GD

How do you go about checking the TPS? What kind of scope does one use? 

I did a 6 mile test drive this morning and it drove perfectly. So I had my daughter pick it up and she said during a short drive it was not entirely symptom free.

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Well ideally you want either an actual graphing automotive oscilloscope. Or you can also use an analog volt/ohm meter. You are looking for dead spots in the wiper of the sensor. This will show up on the graph as you slowly turn the sensor as a sudden drop to 0 volts and then back up to normal reading. You want a smooth transition from 0.5v to 4.5v without any hash or drop outs in the signal. An analog meter can show this as a smooth sweep of the needle. You really can't use a DVOM because it will often miss the drop outs and they tend to switch ranges which also looks like a drop out and can give you a false positive. 

GD

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Put an amp clamp on the fuel pump power lead and if the scope trace drops when the symptoms occur then you can go down that path. Otherwise FP relays aren't a failure item on Subaru's. I can't recall a single failure. 

GD

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Ok, I haven’t had time for a few weeks to try and sort this car out. My daughter has been using my spare car in the meantime.

So today I started looking very closely at all the vacuum hoses to see if I missed something. The hose that goes to the PCV seems a bit loose on one end. Could an air leak there cause major misbehaving? If so it might be able to explain the intermittent nature of the problem. Maybe it seals there sometimes and then other times not.

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No. The hose would have to present a much larger leak than a "bit loose" - it would have to effect fuel trims significantly to cause stalling. 

GD

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8 minutes ago, GeneralDisorder said:

No. The hose would have to present a much larger leak than a "bit loose" - it would have to effect fuel trims significantly to cause stalling. 

GD

Okay thanks.

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Well we took the car into a mechanic that specializes in Subarus to get this car sorted out. They said it was a weird interesting case. After a couple hours of labor they determined that it was an electrical problem. They surmise there is corrosion between the transmission and the engine causing a voltage drop. The  ground cable from the battery goes to the transmission. So they put on a “bandaid” short ground cable from the transmission to the engine. My daughter reports the car is now behaving normally and appears ready her upcoming road trip from Fairbanks to Anchorage in about a week.

Thanks everyone for the advice and suggestions on diagnosing this. I learned a lot more about working on our five elderly Subarus (95-98) as a result of this frustrating problem. It should help me in the future keeping them all going.

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