About a month or 2 ago my car which has a 91 jetta 1.6 NA motor decided to start hesitating only around partial throttle at between 45 and 55 mph. New Fuel filter was installed 4 months ago. Car has an electric primer pump. It makes no difference if the primer pump is on or off. The accessory belt only runs the water pump and alternator. Any ideas of where to start looking would be greatly appreciated.