I have a 1990 Blue vert AT with 109k miles. I have had 2 episodes in past month when on startup white-gray smoke comes from under the engine area next to the firewall to the passenger area (below the middle of windshield). The smoke lasts several minutes and then stops. No smoke in exhaust and no rapid coolant loss. Temperature, oil pressure, oil level, and engine power are fine, car runs great. Please give me some ideas as to cause and cure. Thanks!

 

Thats where the exhaust manifold connects to the downpipe or catalytic converter if your exhuast is stock. Sounds like you have an exhaust leak. Maybe that is what exhaust looks like before it goes through the cats.

 

Yep when it heats up it expands and seals the leak.Get a new gasket for the flange.