I bought it with 132k miles about 1.5 months ago.

Car runs fine.

One week later late at night when it was cold check engine light came on.
Car runs fine. Next morning code reader said "oxygen sensor".
Cleared the code. Car runs fine.

One week later
Was hard to start in the morning, had to push the accelerator pedal - started right away that way.
Replaced spark plugs, air filter, fuel filter. Car runs fine.

3 days later

At a red light knock-knock in the engine, had to quickly shift to neutral to prevent a stall,
drove home, check engine light came on after 2-3 traffic lights, knocking continued occassionally.

next day - starts well, runs well, check engine light on

code reader said 4 codes
Cylinder 3 misfiring
Cylinder 2 misfiring
General misfire
Cylinder 3 misfiring - yes, same code the second time

Read that multiple cylinder misfiring can be fixed by replacing oil control valves

But mechanic said looks like only one cylinder is misfiring and replaced the ignition coil

one week later

Late at night when it was cold check engine light came on. Car runs fine. Next day check engine light is on, car runs fine. Next day check engine light disappears in the morning at first start, so I could not read any codes - was planning to do that that morning.

Two weeks later

car runs with some minor resistance like from parking brake
next morning hard to start - had to step on accelerator, started right away

next morning - started easily, but stalled when I shifted from P to R
after that started easily , runs well

next afternoon - was even harder to start - this time it sat for about 18 hours overnight rather than the usual 10-12 overnight, but stepped on accelerator and it started right away.

started to drive, suddenly "brake" light came on, then blinked and went off after about 20-30sec.
This repeated about 5 times . Car runs with some minor resistance like from a parking brake.

And this is how the story ended tonight.

 

had the same issues ,mechanic changed the VT sensor and Oli valve Control,CEL still came on says P0171

 

I think the cylinder misfiring was a separate issue from the occassionally hard to start issue I am currently having, but I could be wrong.

 

When my 2000 ES300 started developing low idle RPM on initial startup in the mornings that caused stalling unless the engine was hot, I had a fuel induction service done (injector cleaner, throttle body cleaning, etc) and switched back from regular to premium grade fuel. Problem went away.
Ironically, that problem only started after I used my first (and last) bottle of Chevron Techron injector cleaner.