all the things your contributing to an ECU problem seem to involve the instrument cluster too. I would try pulling out the instrument cluster checking/cleaning the electrical contacts, and reinstalling it. Gotta remember that she's 21 years old now and your probably gonna find some old age wrinkles in the wiring from time to time. Start your diagnostics with the cheap and simple things first. In this case, that's a pretty easy and $0 dollar first thing to check.