Well, I had a bad intake manifold gasket which caused a horrible idle but no spike in power.
Give it a complete tune up. Replace the plugs, wires, dump in some injector cleaner, and clean the MAF. Old plug wires can develop microscopic cracks that let them arc to ground.
Have you replaced your PCV? I did mine at 80k and it was insanely clogged up. Yours may be sticking shut causing the problem. You are building up pressure in the crankcase causing it to bog and then it is suddenly released.
You can also check to see if you have a vacuum leak be spraying carb cleaner around the areas that you think you may have a leak. If the carb cleaner gets sucked in by the vacuum leak, you idle will jump up for a second.
HTH,
BP
