new header low rpm idle?
 

I just installed a new header, and now when I idle at stop signs or parked, the rpm drops to 400-500. is this normal? before the header I idled at 1100

No Check engine light came on, I hooked up all the o2 sensors, and I unhooked the battery,pumped break, and waited 30 sec to reconnect after install.

Is that the proper way to reset the computer? could a bad gasket be the cause, because the downpipe to cat gasket fit seemed a little iffy to me, although there is no check engine light.

Also, there was a weird smell, but i assumed it was oil or something burning off the new header.

idle at1100 ? lol it should be 600-700

Sometimes you need to drive the car for a while for the ECU to relearn the idle after resetting it. But yes, your previous idle seemed high.