BMW has quite a few engines worth checking out for a potential swap, and the M42 and M44 are two decent four-cylinder picks. They aren't known as the most reliable BMW engines ever built ...
The Bimmer M44 engine in this car was built for a short time between 1996 and 2000, it’s basically an updated version of the DOHC four-cylinder engine that had been in E30s and E36s since 1989.