I was thinking catalytic converter too...some bad stuff going through can clog it up and mess it up...you may be in for a new one down the road or sooner than you think and they are not a cheap item. Another thought along with this is the fuel filter. If not changed yet, I would recommend changing it out and see if that makes a difference. It too can get clogged causing some of the symptoms your car is having. I would syphon all of the no-name gas out and refill with Chevron Techron or similar grade of good gas. The white smoke your describing sure sounds like water vapor in your engine. Keep an eye out on temp. guage as well as any new codes. You don't want your engine messed up on the account of some bad gas. Good luck
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.