i'm having exact same problem as you are. I can't figure it out either, i've replaced the o2 sensor, i'm trying to find an engine temp sensor, the parts dealer said they don't have any

my ECU says mine is bad.

this car is making me crazy. The only difference in mine and yours is when your near redline ur car smokes, mine won't smoke unless i've been idling at a light and give it gas, its not dense smoke so i don't beleave its coolant, i go through oil but not a quart a week. My plugs show normal wear and no sign of oil leakage.
Car feels sluggish, at time when i'm at a stop and give it gas the RPMs Drop real low near 500 and it pops-up. I don't think its a fuel pump problem i replaced my fuel filter w/ 300zx one no change still dose it.
Have you tried compression testing your motor? Good way of telling if your rings are bad. I will do mine shortly when I get enough time.
I'll keep this post in favorites if i run acrossed the problem, i'll share it,
And with your o2, its a 1 wire sensor, mine was rusted to crap so i went to home depo picked up some connectors that looked like the stock one on my car, spliced the o2 wire into the male side and the body to the female, worked for me.
I have SOHC also so, our problem has to be simaliar.
"i'm real sick so i'm not gonna proof read so if there bad mistakes, its cause i was to lazy to go back and check

"