Hey my brother has a 1990 Nissan 300ZX that every time he decelerates (sp?) white smoke comes pouring out of the exhaust. Could it be in his valve seals? That was my thought but someone said it could be a water leak somewhere. What do you guys think?

Also, it's a twin-turbo car

Valve seals sound pretty likely. One thing for sure , if its steam you'll know cause you will always be adding water with no evidence of a water leak.

Besides when you get water leaking into the exhaust it makes more steam on the throttle than off for obvious reasons.

Valve seals?? I don't envy you that job on a twin turbo model.

head gasket

Yeah I had a feeling it was either a valve seal or gasket...don't worry, I already told my brother I'll never help him as long as the thing is twin turbo! lol Still trying to get him to trade the thing in for a 94 corvette, but he's really stuck on the turbo idea...we'll see if he still is after this!