several options:

plugged cat as mojo mentioned (easily tested by driving in 2nd gear, mid revs for @ 5 minutes, climb under and see if it is glowing redish. (not all together scientific but it did help me diagnose my vw a few years ago)

plugged air filter/ air inlet. Make sure your intake system is free and open (mouse nest, dead bird, anything in the chain

computer related issue. same vw had one bad computer box that we could only diagnose with the use of a hair dryer (heat the box to simulate road and engine heat and it would fault out).

balance of fuel system issue. Clogged injector, fuel line, fuel line screen (if there is one)

typically the big two, fuel and air, are easier to diagnose. the other item would be spark (plugs, wires, computer related).

good luck