Anybody have any idea wtf this might be?

Originally Posted by nismo2evox

^Is it possible the previous owner tuned it in any way which is causing the problems.

I've heard of some shops around here doing an "uprev" tune to the Z's and can screw it up.

Also, are there any signs of modification done previously?

Not to add to your paranioa but someone could be that someone screwed with the car, started having problems, got it fixed enough to trade it in. Do you /the the dealership have the service records on the car. If the basic maintenance wasn't done at Nissan, it could have been done by the previous owner or a tuning shop.

I used to bring my Evo to my tuning shop for oil changes instead of Mitsubishi.

Hope everything works out. Do they have lemon laws on used cars where you are from?