vacuum leak or injectors? Or both...?

[sachsy]

I run VERY rich. Black, wet smoke rich. Better once it gets warmed up, but still not great and, if I kick it down a gear, it comes with a black "puff"...

Further, occasionally when I first start cold (BTW, cold starts are easy) it sputters and coughs at under 500RPM. Once warmed, this does not become a problem again...

Vacuum gauge on the fuel economy is pegged left in P and N, but hovers at about 1/4 once in gear... Bought a vacuum gauge and tested by the brake booster--holding the gauge by hand--no perfect seal there--it read ~19.

Any ideas other than the mechanic's (which was to spend 10 hours of labor looking for the vacuum leak) would be appreciated.

I bought a bottle of techron to add to the fuel as well, with the thought that it may help clean the injectors if that is, indeed, the issue. Anyone have an opinion on that? Will the additive do more damage than good??

I'm still learning to feel my way around the car, so any ideas or advice are appreciated!

THANK YOU!