When's the last time or have you ever replaced the following:
- the "rotor button" (located inside of the dist. cap)?
- spark plug wires?
- coil?

If it's been 1.5 years, it's about time for another set of spark plugs anyway. Some may say differently, but it's a good idea to do them every 2 years. And don't use crazy stuff like Bosch Platniums and Split Fires and all that crap. They don't work and actually can make your car run rough. Bosch Platniums caused my 95 to run like shite. Just used good ol' NGK.

If you replace them, use quality spark plug wires too. I've had a cheap, thin set basically melt on my car...

Have you inspected your dist. cap for scarring or cracks, etc.

Does your 98 REQUIRE high octance only?

When's the last time you adjusted your valves? It's a pretty easy DIY too.

Go through all of that first.