Well the exhaust still has a cat on it and it still passes emissions I've also been told that it's probably the the gasket on the header. I have no clue really or if I need to go to the dealer to get the gasket because autozone and advanced don't carry the gasket. Any other way I can get it? It's only like 5 bolts holding it on plus the exhaust was loose the weld had come undone and I don't think they replaced the gasket when they put the headers on. The guy at the shop said it was a common mistake he had the same problem with his supra. I only smell it inside when the rpms are high. The temp usually stays pretty low to normal so I am not sure the intake is causing too much of a problem.