Car sputtering and excessive white smoke ..is cheaper to swap or fix.

Do you have bubbling in your coolant and milky oil? If so, it is likely a head gasket issue. It is generally cheaper to swap with another motor, but if you don't know the history of the other motor you could shortly find yourself in the same situation. I personally would fix it.

Check out www.rs25.com, it is specifically for your RS and has lots of info.

I wouldn't say it's cheaper to swap a motor than fix a head gasket if that is the issue. Especially if you can't do the swap yourself. Headgaskets aren't too expensive and it gives the chance for the rest of the rngine to be looked over at the same time and from that point on you know you're good for a long time. Most replacement engines come with a 1 year warranty max if that and never quite run the same as the origional.

Not saying it's smart at all, but people who just swap a junkyard motor in without going through what they should to refresh the engine tend to end up paying less. One thing that can really drive up the price on fixing a head gasket is having the heads planed if the motor has been overheated.