So I have a 2001 cobra convertible and recently my car has been acting up. When I turn it on and it's sitting at idle the car shake viciously and it does every time I go to neutral or stop say at a light. My rpms are idle they aren't bouncing around. And I get a flashing check engine light at higher speeds and when I slow down below 40 or so the light goes away? I already changed the spark plugs and I don't know what else it could be coil packs or fuel injectors ? Need HELP!!