I had them installed at an exhaust shop, and Im not too confident in the quality of the installation. Its making a weird rattling noise whenever I drive, and it seems as if the car is almost slower now then what it was before. How much do headers take off top end? My scanner read 7 degrees of KR at full throttle, at about 57mph, and the check engine light came on, and at one point was blinking. At that point I have seen enough and decided I didnt want my car to blow up, so I came home immediately... Something aint right. Im going back to the exhaust shop tomorrow, and telling em whats up. Anyone here have any ideas?

Edit: Argh, forgot to post code... The code on my scanner read P0300.

P0300 is Misfire detected. Check to make sure all your spark plug wires are snapped in and in the proper order.

Blinking SES light is a hard misfire. As stated already, check plugs and wires and firing order. Headers will improve top end but will lower low end feel.

Now that you have better flow you don't have as much back pressure so your low end torque will drop off. And the noise; I have a odd noiseI can hear inside my car but nothing can be heard from outside, one guy I work with called it "A exhaust pulse" common to headers. Would be a first to me on that one but I can't find any leaks so I'm gonna trust him.

They shouldn't take anything off of the top end they should add to the top end power.

You want to allow time for your pcm to adjust to the new flow and such. I would also crawl around and look so see if anything is bumping into the headers like power steering lines or heat sheilds as that could cause false knock (I would think.) Check and double check your plug wires. Try to wait a day or two and rack up some miles before you go back to the exhaust shop.

Ed