[W126 Coupe] White smoke plus missfire update

[Pavel]

Here is the update on my 560sel.  After raising the fuel pressure on the
eha valve and running a few tanks of fresh gas the idle is smooth.  I do
suspect a vacuum leak somewhere because the economy gauge is not all the
way to the left at idle and when coasting at 40 the rpm move around
slightly and surge car forward than slow down.
My next problem is white smoke.  After a long drive on highway when I come
to a stop it lets out a cloud of fog.  Or if I accelerate very hard and
stop fast it will release a cloud of smoke when I slow down (using the
brakes not engine).  As soon as i put some load on the motor the smoke goes
away.  I figured that it was a tranny modulator and replaced it made it
smoke less frequent but still does it once in a while.  I do not burn any
antifreeze or oil (less than a quart of oil every 5k miles) Could I have
bought a bad modulator? Or is this connected to my vacuum gremlin? BTW I'm
using mobil one synthetic tranny fluid. 
thanks
Pavel