Hello all, and thank you for any assistance you may have. I have a 99 Mazda B4000 4X4 with 103500 miles on it. I recently had a check engine light come on ( a week ago) an the code was, #1 Oxygen sensor. At the same time, the hesitation while driving and at idle started. I was doing about 65 mph when this all started. I replaced the Oxygen sensor, and reset the check engine light, by removing the battery cables. The problem still persists, so after a little research, I cleaned the "Mass Air Flow sensor". That drastically improved performance. For about two days, than it returned to the poor performance. I have now replaced the ""Mass Air Flow sensor". On first staring the truck, idle ran rough, and had some hesitation. Drove a few miles, an "Wow" problem fixed.... Sadly problem returned, prior to making it back home. So we have; Rough idle (stars fine, runs fine, gets rough, then ok, then rough again) Hesitation or jerky when driving at different speeds (all most vibrates you out of the seat at times) If I stomp on it, it gets worse, let off an it is fine for a bit. then starts again. No Check Engine light.