[Overdrive]

Unfortunately we're just as blind as you are in this since you don't have access to the car, and you're the one we're in contact with.

If the smoke came out of the passenger side, as someone mentioned here, you may want to check the air-oil separator. They tend to give up the ghost at random as it is, and I'm sure some form of explosion in the engine compartment could help that happen, and a bad AOS is going to leave the car running poorly, if it runs at all. The only thing throwing me off from looking at the AOS as the culprit is that you're saying the car runs fine at times. Does it run fine like how it always did, or just run a little better than the really bad limp mode?

Kind of obvious, but just so it's said, tell your brother not to start, move, or drive the car until it has been looked at. If there's something seriously wrong, you don't want to keep running the car and make it worse.

Keep us posted on what you find, but unfortunately we really can't do much just based on what's been given so far. Be ready to take and post pictures of what you see when the engine bay is accessed, and folks on here can do a bit less shooting in the dark. There's really almost no point to us throwing a dozen theories out there instead of just waiting to see the situation and what you're really dealing with. Searching online without having that information and the car right in front of you is just going to fill your head with a million possbilities and stress you out.