93SIRII

Has anyone had a problem like this before, my car sometimes losses power between two and four thousand rpm it feels like its going to die then all of a sudden it comes back into life again. The guys at PE tuning are stumped we have tried everything the ignition timing is right the plugs are fine there is no vaccum leaks they think it could be a computer problem or possibly the O2 sensor. They have felt the bogging out of power when it was on the dyno and its only making 140whp it has air intake, CTR intake cam, cam gears, magnaflow exhaust(no cat) and fields vtec controller which has been set and still doesn't help

HELP I have no ideas?