Could be a faulty sensor. When I had a similar problem, it was my front abs sensor wire touching on the hot disc. Put it back in the clip and taped it all up and been fine since.
I've read before that when they are bored out this far, it makes the wall between the pistons and cooling channels a bit weak. I've seen 2 on eBay in the last week. I would guess they would be ok to run na but I wouldn't go forced with these engines personally!
My pipercross is behind the bumper. It's really small and fits just behind the receiver / drier. It had to be small because my maf is there to but mine comes off the charger.
It could make a bit of a difference but you need to know what faults your cars showing. You might plug a maf in and have the same problem and it could be there's nothing wrong with yours or the donor maf. If you disconnect your battery for around half an hour your ecu should forget the learnt values and start from scratch. You could do with checking which diagnostic port you have in your car too. Take your ashtray out and the little rectangular plastic bit to the left of the ashtray should slide out to the right. If you have a 16 pin plug there then a normal obd2 cable will be ok for diagn
Mine did similar to that once and it was the lambda! Mine is charged though and I was having running problems at the time. I changed everything. Maf, plugs, leads, lambda, injectors, throttle body, air filter.