I have similar symptoms. In my '90 300zx
I did an injector swap this weekend. Idled it in the garage for 10 minutes, no issues. Did a mile loop. No issues. When I started the car, it was almost instant-on. You'd just think about the ignition and the puppy would fire up.
I was driving home today at about 50mph and i spied white wispy/billowy (not opaque) smoke in my rear view. I didn't notice any sounds or vibrations from the engine. Turned off the road ASAP. Engine died when I put in the clutch to downshift, restarted when i let the clutch out. Rolled to a stop some 200ft later. I can't remember if I shut off the engine at this stop, or if it died. There was still a little bit of "smoke" (more like vapor or steam) coming out the right exhaust when I went around back. I quick went down for a smell. Not a hint of antifreeze smell. It smelled heavily of fuel. A few seconds later I could see the wavvy lines associated with evaporating fuel coming out the exhaust tip. I pulled the relay for the fuel pump to ensure that if there was a runaway injector, it wouldn't have pressure to work with.
Got towed home (not far... but bless AAA). I let it sit for a couple hours and read a few forums. I checked the oil and it smells a bit of fuel. The level is above the hash marks. It was last changed by the nissan folks, so I hope they're capable of not overfilling. It wasn't putting out smoke before the injector swap, anyhow.
So, I have similar symptoms so I thought I'd ask also if you can elaborate on what you changed on your "tune up" to get things working. I know this thread is a couple years old, but hey. Why start a new one for the same symptoms.
I'm thinking it could be a stuck-open injector. A pinched o-ring is possible but I was SUPER careful lubing those suckers up and putting them in. Also, it was a sudden issue that only manifested after ~10 miles.
Also, everyone hope with me that nothing got bent.
Other thoughts welcome. I suppose an oil change at the very least will be needed. I'm leaving it for the night to let my fear/sadness/anger/stress subside so I don't get grabby.