Quote Originally Posted by scottydoggs View Post
your cat could also be getting clogged.
Quote Originally Posted by dsmuts View Post
rotten egg smell is clogged cat for sure.
Quote Originally Posted by scottydoggs View Post
it can cause misfires, which is what you are feeling when it wont go past 4,000 rpms, the cel light should be flashing when you do this, flashing light means stop doing what your doing.

if you can get your car in the air, ramps, or jacks, hit the cat when its cold, listen for stuff rattling around inside it.if so its shot..
Quote Originally Posted by Neil98gt View Post
its probably the cat, if it smells like rotten eggs, like stated before.

When the car is cold jack it up and tap on the cat. If it rattles, its shot.

and no it doesnt have to be from all rpm's for it to be the cat, just when it flows enough to cause a problem
I think you have found your problem.

Replace your cat