Single white Female.... has a sweet 1999 Subaru Outback Impreza, manual. The check engine light is on all the time but the car runs perfectly! Every now and then the check engine light blinks - seems

That's not the problem , Check all electrical connections carefully

2000 Subaru Impreza Outback service manual calls for 1.0 mm to 1.1 mm or .039 in. to .044 in. Most spark plugs at any auto store should be pre-gapped, but double checking never hurt. Make sure to apply a very light coat to the spark plug threads and torque them to 15 ft-lbs +/- 2 ft-lbs. Good luck.

First check for an owners manual(it will say), if there isn't one a lot times there will be a sticker on the inside of the gas lid saying what to use. However, unless to vehicle is turbo or is higher compression than stock, i am quite certain 87 octane will suffice.

no adjustment, computer controlled, you're problem rests elsewhere, do a compression test,

Below is a link for the wiring diagram you requested:

2002 Subaru Outback Wiring

If you have any of the large chain auto parts stores in your area, call them and ask if they do free scans; most do.
If Subaru has maintained the same procedures for a while, and you have checked fluids, etc., you can try resetting the light via the ignition switch:
-Turn on the ignition (don't start) - switch it rapidly between the 'ignition on' and 'ignition off' positions three times.
If the error has cleared itself (not uncommon), the check light will reset. If the problem is still present, it will either stay or come back on.
Our Su has done this a couple of times and with the scanner we have on hand, there was never any particular repeated problem. Just a computer glitch/hiccough -

Please confirm year, make, mode,l & engine. Thanks

check all grounds

It will end up in the intake and you should be getting white smoke from the exhuast

directly below the throttle body on the drivers side of the engine block. Has a white connector attached to a single black wire lead. I had to remove the black plastic piece that connects to the throttle body and the air filter housing, in order to see/get at it. Easy fix once you find it. Haynes manual shows it in a different location, so don't confuse yourself looking at the diagram.