Nissan Maxima

I own a Nissan Maxima 1995 V6 3.0 lit car. It is currently 113000 miles on it. Sometimes when I start the car during cold conditions the car does not start immediately. I have to crank up the gas pedal and turn on the ignition to start. Once started it vibrated for some time. If I pump the gas pedal during that time it becomes normal. Initially I thought it could be due to o2 sensor. And after I replaced the o2 sensor still the problem persists. Any idea what could be the problem? If it is due to battery, which I dont think why there is vibration before the engine runs normal?
June 19, 2006.

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