Garage Cabinets, Garage Storage, and Garage Organization

I am having a 1996 320i. And for no apparent reason the engine has gone too slow and sluggish. bmw hasn’t given me any major troubles since last 4 years so I am not planning to trade it for something better. But yeah if there’s any good advice I can have on how can I increase the engine efficiency. Thanks in advance.

increase engine eficiency is one thing and I dont have a clue. But engine has gone to slow is an other and with manu options cheap or expensive
cheap as air filter - fuel filter - sparkplugs . expensive as clogged catalytic converter.