problem after install header

i have a 96 sunfire 2.4 i installed a header now when the car sits it will start fine but when i go it will hesitate and fluter for couple of seconds then it ok until i shut it off and let it sit again.

im lost on this one

ps it is a standard and i already cleaned the throddle body

When you replaced the header, did you also replace the O2 sensor? A faulty O2 sensor can throw the computer off and make the car run rough. I'd definatly replace that if not already done so.

when i bought the car it had a new o2 sencer in the glove box, so i put that in with the new header. but maybe ill try a nother one, there not that much money. as far as derbying it. it a convertible. and i dont derby anymore.
but if derby is your thing here is what i used and last 15 1/2 derbys.
get an old monte carlo or grand prix around 1975 with a good frame(hard to find) if the engine runs use it until it goes. but then put in a v6 early 80 cars. at time there was no oil or water and the thing just wouldnt die.
a couple mods and some weilding and your set.