Wow just installed a DC header on my 04' celica GTS. Somewhat difficult because my car has an EGR incorporated into the old exh. manifold. So there are four small exhaust ports above the regular exhaust ports. I took a 1/8in. pipe tap and tapped the small ports and plugged them with 1/8in stainless steel pipe plugs. I reused the gasket, Installed the header and everything sealed up just fine. It does set a code but my check engine light has been on practically since I got the car so it doesn't bother me that much, plus I lost like 5lbs. of weight by removing the EGR and the small turbo looking thing connected to it. My mom has an 04' GTS and hers also has EGR so I assume all '04's probably do. :uhoh: