My 2000 ZX2 has 256k miles. It has what I will refer to as an acceleration stumble when accelerating anything more than mildly. It will stumble/hesitate/jerk while accelerating. It runs smoothly at a steady speed. I have noticed this occasionally in the past and usually when I had the AC on, but it seems to have gotten worse, AC or not. Any ideas what could cause something like that? Thanks in advance for your help.