Per factory spec, they are to bereplaced at 60k miles. I didn't do mine until 80ish, and I waited too long.
You are correct as to what you'd expect to see w/ bad caps & rotors-really sounds like yours are new, though.
Change your O2 sensor (early cars have 1; later cars I believe have 2)...then, what I'd do is pop open the CAN box (where the battery is usually), remove the LH module for 10-15 minutes, then re-install. This will re-set your fuel injection, and you will go to full rich; your car will then begin to adapt itself, slowly.
"If everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car