Your catilitic converter may be plugged with dirt and junk. this happened to my friend's BMW 318IS. go get a universal cat at any auto parts store. it should cost you about $60. One word of advise...
it would have 2 b a exaust leak or the little hose going 2 your breather element isn't attached properly
could be your cat as wellDamaged or restricted exhaust system components; Restricted,...