Air + Fuel + spark =
... especially when you can maintain 14.7 parts air to 1 part fuel. Any other ratio starts to get : | or : \ or even : (
I think with the filter removed you've settled that it's getting lots of air. A stuck injector
could produce the problem you described, along with a whole lot of black smoke from the exhaust from running too rich... but I'm with A-series on this one.
Do a new distributor cap, rotor, wires & plugs. If that doesn't solve the issue, then look at the more expensive parts that are less likely to wear out (like the MAP and TPS). Essentially, the parts listed above are a tune up without a new air and fuel filter, and are usually the #1 causes of poor throttle response.