Usually bad intake valve seals cause a puff of blue smoke on startup, then at highway speeds if you lift off the throttle quickly.

 

All this is good information, but I cannot recall anyone here on the site reporting that they had bad valve seals. Common Chevy problem? Maybe, but this engine is (mostly) not designed by GM.

 

In all my time working on Ecotec engines, I’ve only replaced valve seals when replacing bent valves, because they came in the head gasket kit.

 

I do notice the cloud of smoke when letting off the pedal hard. Does not happen when I still have some throttle. I'm not sure if this matters. Its only when I go from psi to vacuum. Sorry not familiar with turbo motors. A lot to take in.

Unrelated (posted a new thread) would a bad cat cause any of this?

 

No, it wouldn’t, but this could cause a bad catalytic converter!


Good cat!