intermittent black smoke

[Jean-François Roldan]

Hi all,

For the past 3 days, I have been driving along fine on the highway when all 
of a sudden, the engine loses power a bit, hesitates, and clouds of black 
smoke are clearly visible... the back of my car is now all dark from it. 
Then it goes away like it came, power comes back, pedal response too...

And a few minutes later or 20 minutes later it starts again... power drops 
but speed stays around 50-55 mph. When it is smoking like that, if I try to 
accelerate, there is no throttle response, just more smoke... until all goes 
away and it is back to almost normal...

any ideas? could it be timing related? TB was done almost exactly 60K ago

JF
91 200 tqa, 210K