statman24

For almost a year, my 2000 LS400 would smoke at startup in the morning, or after it's been sitting for a while. I just assumed I had leaky valve stem seals. It was definitely oil smoke, as I would have to add oil from time to time.

A few months ago, I started getting check engine light coming on. I don't remember the number, but I did know the cause was a bad upstream O2 sensor on the driver side. I assumed that the burning oil probably took out the O2 sensor.

When I began looking for the location of the o2 sensor, I noticed that the PCV valve was hanging loosely off the engine...because the grommet had fallen apart. So, I replaced the grommet, PCV valve and O2 sensor. The check engine light went out but more importantly (and very surprisingly), so did my smoking problem.

I'm certainly happy about it... but confused. Any thoughts why that would happen?