Engine Performance problem
1991 Nissan 300ZX 6 cyl Two Wheel Drive Manual 180,00 miles

My 91 Z ran absolutely smoothly until one day it just ran like it had one cylinder running poorly. Nissan dealer did a very quick look at some plugs while working on something completely different and said it was running extremely rich. This jibes with the ECU that indicated that something was wrong with the engine temp sensor. One very cold morning, it ran as smoothly as it used to, until after it warmed up (about 3-5 min.) and snapped right back into it's rough state. This wouldn't be much of a problem to fix if I could just learn the ETC's location. This is NOT supposed to be the same as the engine COOLANT temperature sensor which I replaced just in case. I've actually found the part but no manual ever says where it is. I've really been looking and found nothing helpful.