Misfire?
 

Hey everyone, i have a 2005 mazda3s 2.3 hatchback with a 5speed. Recently when I first start the car and the engine is still cold i've been feeling a violent shutter when shifting gears, and the car really seams to have a misfire and struggles in the lower rpms. Once i've driven the car for a few minutes and the engine is warmed up, all these symptoms go away. no check engine light is lit at any time. I tried replacing the spark plugs, but still no dice. The car has about 107xxx on the clock. the only modification the car has is a Magnaflow CBE. Does anybody know what could be causing this? anything is appreciated.

headley, very useful advice. Misfire could be caused by bad spark plugs or bad air flow sensor. Unfortunately only service shop can determine it I guess.