11-05-12, 11:56 AM
I have a 2005 STS with the Northstar engine. It is not accelerating properly. This problem started with hesitation and bogging down under rapid acceleration. So I replaced the spark plugs with DENZO brand recommended by my auto parts store. I also replaced the fuel filter. Since then, the lunging under acceleration has gotten worse. It generally happens in the lower gears (1st and 2nd). The car will bog down under acceleration and then kick forward with an awkward lunge. This pattern continues repeatedly under acceleration. Once I reach road speed, and the transmission is in 4th or 5th gears, the lunging ceases. I need some help!