The rev hang or skip shift isn't about unburnt hydrocarbons, it's about efficiency standards. It's a different problem - emissions efficiency is one thing and emission compound/type restrictions are another.
Incorrect. The engine speed hold is there to optimize mixture while the engine decelerates, instead of just slamming the throttle shut. Depending on where the fuel is injected, cutting off fuel and air instantly leads to either too much fuel or too much air in the cylinders. The electronic rev hang corrects this to reduce NOx and unburnt fuel. It does not improve fuel efficiency.
The difference between DI and port injection is only which thing is escaping the catalytic converter. With port injection the engine is rich after lifting off the throttle, and hydrocarbons escape. With direct injection the engine leans out, and NOx escapes. In both cases the rev hang exists to keep the emissions system in its effective air/fuel ratio range. Every hanging MT car I ever owned was DI.
That's very odd. DI should only be firing a full shot injector as the air is coming in, or already came in. It really shouldn't lean out. If your DI car had rev hang, it's for other reasons.
We were discussing the 2015 WRX after all, it is port injected. The guy who wants to delete the rev hang from his VA WRX is advocating to blowing unburnt gas right out of the tailpipe, like a psycho.
