My car starts up and runs fine for about 45 seconds, then the idle starts to drop and get rough, then it dies. When I start it back up it dies again after a couple seconds, and so on. I just drive gently until it gets up to operating temp, then it's completely normal. Even when sitting at a stoplight it idles fine. So whatever it is it only does it when the engine is cold. This only started happening after my recent header install. Any ideas before I have to get my hands dirty? Thanks. (Mods in sig.)