I noticed on my old engine my car would spudder when i shifted. It always seems to like spudder around the 2500-3000 rpm range. Could this problem be my mass airflow sensor or maybe the o2 sensor??? So I was thinking that its probably something that i brought over from my old engine, such as the cold air intake and the o2 sensor. I've just had it with this nissan, if i cant figure out whats wrong with this thing, you'll see it in the "Cars for Sale" section.