Subaru Repair: 94 Subaru Legacy Turbo wagon, rocky mtns, car mom

Question
Hey!  I love this site!  So, my newly acquired turbo is doing a few things that concern me/need repair.  She used to live in the Rocky Mtns. where they tend to change the idle due to the lack of O2 in the air at 10,000 ft. Now she's living on the coast in Malibu, Ca.  Bear with me, here's what's going on... 1) Sometimes it will crank fine, but not turn over.  Mom used to own it, she says nail down the gas peddle (can't be good) but it worked until recently, now it usually doesn't and if it does it usually stalls out (flooding it?) and a lil' fuel smelly white smoke puffs out the tail pipe...most likely suspect(s)?  Yes, I am infrequently, but daily getting a check engine light.  2)Sometimes it revs up like it has idle issues when I'm at a stop light, or won't idle down when I park after driving (usually followed by #1 next time I try to start it).  Hmmmm.  3) There's a small black box in the very front of the engine near the headlight on the passenger side of the engine that runs sometimes (15-20 mins) when I turn off the car.  Mom says smack it and it'll stop, she's right, it does, (again can't be good, Ahh..I love my mom).  What is this box and got any ideas why it's doing this/should it be?  As for 1&2 could this be issues related to the way the idle is set or they separate issues?  Clearly, I'm a woman, so I've found it helps to know a little before I go to the repair shop, lest I'm spending a fortune and fixing nothing, (go ahead and ask me some questions about '87 F-250's).  I'm clear that I need someone to check it to see what codes it produces, but I still would like a little heads up.  Lay it on me, I'm "listening"...

Answer
I looked into it and the source material I have doesn't give me a clear idea of what that little box does. The good thing is that you do have a check engine light. There is a BARO/MAP switching valve near that location next to the air cleaner. Judging by the fact the the car is from a lower altitude and is now in a higher one, it is exhibiting the symptoms of not sensing and/or compensating for the barometric pressure difference. I would have the computer scanned to verify it but that sounds like a likely suspect.