I have the same problem on Is200D 2011 (90.000 miles). It smokes (clouds of white smoke) just before the temp guage reaches normal). Deisel consumption 45MPG on motorway and mid20s around town. Plugged in computer but no error codes. Otherwise this car has been problem free.
I have decided to change the exaust temp sensors(2) as it appears to be related to engine temperature. Bought them for £300 on line and am awaiting delivery. I will update progress.
I previously had L dealer investigate the problem. They siad it was the oxygen sensor and changed it for £350. It made no differance. They then suggested a new DPF (my one had just been cleaned), so I too have abandoned the dealer for a solution, they can only look at the computer and do what is says!
Lexus is not acting responsibly with this problem. They must by now know the cause of the problem and should update their error code system. Clouds of white smoke coming out of otherwise pristine Lexus cars must damage their immage. It screams "dont buy a Lexus"
