I had a similar problem with a piston engine car where I was getting air pushed OUT through the TB instead of having suction as it should... Turned out to be an extremely clogged catalytic convertor. Thing was actually clogged so bad that the engine would not even run! Pulled out the O2 sensor and it was able to start but dies when a chunk of the bad catalytic convertor plugged the O2 sesnor hole.

That car was a puzzle for a few days in the shop. Got the catalytic convertor replaced and all was well... After we fixed what caused the convertor to go bad in the first place (plugs, wires, bad tps, bad map sensor). Bad wires fouled a few plugs, bad tps and map caused fuel conditions, plugs couldn't burn extra fuel because of bad wires, extra unburned fuel breaks down convertor, plugged convertor causes all sorts of hell and makes for a very frustrated tech! Oh yeah, fuel pump being bad didn't make life any easier either (25PSI peak).

 

Brand new hi flow 3" cat. Was put in 2 weeks ago with brand new exhaust system..