RPM's dropping below "normal" at idle
 

So, when I'm sitting at a red light, my car will make an engine "clunking" sound, just once or twice every 60seconds, where the RPM's drop quickly, then come back to normal (around 6-700). Spark plugs?
Thanks in advance for the input.

what other variations affect the symptom? temp? patterns of when it occur the most? i don't think spark plugs would affect it in the pattern you have described

Could be a plug, or a coil, or a few other things.

CEL on?

I see you're a '99...still on original coils? There's your problem.

I had a similar problem without the clunk on my 96. The plugs (Autolites)
looked in good shape, but I replaced them with NGKs, and that fixed it.