I've been experiencing something similar recently with my '96 Accent:
An intermittent, noticeable loss of horsepower. Usually on
acceleration, but occasionally at highway speed. Codes checked clear,
fuel pressure ok, replaced plugs and wires (needed it anyway), replaced
fuel and air filters. Ran out of ideas and took it to local shop, who
cleaned... emissionssomething (lost the receipt, doh!).
Acceleration improves within 2-5 seconds of the power drop, but I'd
rather it work properly. Seems to be weather/temperature independent,
but I've not tracked that too closely either. No rough idle nor smoke
out the exhaust (nor anywhere else for that matter).
Thoughts?