engine intermittantly loses power when fully warmed, happens more when cruising at around 2500rpm. there is some lurching and a very rare stall. have changed plugs/wires/cap/button, change oil every 2500 miles, keep sea foam in every 6 months. just noticed white smoke from just before what i believe to be flex pipe on exhaust near the front of the car. bad gasket? could this be the result of power fluctuations?

 

there is a chance based on what you've described for the drivability issue, that the catalytic converter has become clogged to some degree. if the bolts aren't too rusty it's easy enough to pull back and have a look with a flashlight. you'll want to look at the upstream side nearest the engine.