What are some.... Can I visually check?

If you have an a/f gauge, then you can see it responding slower than normal. Otherwise, you could use a multimeter or datalogger to monitor the a/f voltage (just like an a/f gauge). But it's kinda hard to tell how slow is slow, and what's normal fluctuation. If you think it's dying, just get the NTK o2 sensor from nopi for only 45 bucks shipped. It's a good thing to replace every couple years (I'm already on my third one because my old ones started dying and responding slowly).

Well Dan (Sd_Eclipse) hurry up with my A/F gauge ;)

Well when idling it felt like the car was going to shake to death. I only had to drive home about 2 minutes so I parked right away and havnt started yet today.

I also got a CEL blinkin on the way home.

Crappy gas milage also is a good sign.

Check the CEL doing the key dance, and if it's 21, then it's your o2 sensor. But I don't think a dead o2 would cause such severe symptoms all of a sudden. It might be something else...check the code to see.

I thought the key dance was for 95-96?
If not what do you do, sorry for the newbie type questions but I seriously have never had any trouble with my car in 43,000 ;)

a bad o2 signs you might see, gas miles, air/fuel not as fast as before or i believe you can test it with a multimeter with the car running forgot how it goes, but my cel was blinking when i was crusing on the freeway in norco with eric c and my car wanted to die! it was not funny the car lost like all power but left me some to try to pull over... to this day i have no clue what happen.. its ok now my friend james just hit a couple crap and the car runs fine again... =(
Michael 99gs- hrc stage 2

yeah, check with obd-2 software, a multimeter, or a/f gauge.. they usually read lean when they go bad... i replace mine regularly cause of leaded fuels...

Key dance works for 97 for me, I think also for 98 too. Check 2gnt.com under Mods I think or Info to see the howto.

some of the symptoms would be bad idle, loss of power (bogging), and cel.. those were the symptoms that i had

Some symptoms of mine were.... wait I didnt have any cause I use one for a A/F gauge and thats it.. hehe DFI. Butit'll piss you off when the a/f gauge doesnt go blinky blink blink anymore...