[hate2loveford]

The magnet on or near the engine control systems brings up an alternating theory:

A wire or wires vibrating near a magnet. Wonder if a fuel injector wire set could do that... If it did, then a resulting current would be induced. That will likely never have enough current to open an injector, but it could easily keep an injector open, for some infinitesimal time longer than the ECU intended. A rich condition could be detected by the O2 sensor. The ECU would reduce the pulse width, leaning out the engine, at least a mild lean condition on the other cyclinders.
A TPS or temp sensor could be getting an alternating signal. More bad signals for the ECU to sort out.
Magnets, near vibrating wires, is not the type of thing I would do to MOD my car.
A more plausible explaination would be a cleaner or cleaned cat. Cleaner or cleaned O2 sensors. Just those two simple things can result in a car "Acting" like new again.