91 MR2 NA hesitation problem

I have a 91 NA MR2 that has had an annoying hesitation problem since I bought it months ago. The car will usually run just fine when first started in the morning or when cold and the idle is still in the kicked up mode. But as soon as the engine warms up a notch I get a momentary hesitation, almost a lugging feeling and then the power is okay.

I've already done all the tune up things, plugs, wires cap and all that with no help. Some people have suggested resetting the ECU, and that doesn't help either. When you goole this problem it appears as though lots of people have the same problem, many even say they haven't ever fixed it, but nobody has a solution.

My only thought is maybe the TPS is bad or out of adjustment? other than that maybe a bad ECU? I have never had the check engine light on though...