I have a 1988 Chevrolet G20 Van with a 5.0 Liter tbi V8 engine that has 137000 miles on it. The Van runs well except for this one thing. no matter what your speed whether you are stopped at a stoplight or going 55 down the highway as soon as you step on the gas and try to accelerate the engine will cut out briefly for one-quarter of a second or maybe one-half second and we hear a loud noise resembling a backfire at the very same time. it's like the engine actually "coughs". if you keep your foot on the gas and keep accellerating it will cough again every 3 to 5 seconds or so and will keep doing this until you take your foot completely off the gas pedal or the engine catches up to your desired speed and levels off. when you are going down the road at a steady engine rpm none of this stuff happens. We just replaced the fuel filter and now it runs even smoother at a steady rpm. What gives? Ignition system? Vacuum advance? Fuel pump?!?!! i'd like to hear your ideas...