Due to the fact that problems appear to occur when the engine torque is increased, I would tend to suspect the problem is related to your ignition system, i.e., plug wires, distributor cap, rotor, plugs. If you have around 100k or more and any of these parts are original, change them out regardless of your code. For a car this age, I would also replace the fuel filter and closely check vacuum hoses. These are simple things you can do yourself and save a bundle.

good luck