I dunno, my setup has served me pretty well over the years... my continued education into Boost, lol. I do have a SAFC to trim my fuel @ idle, but it shouldn't be necessary at all (I would assume you would just run rich @ idle without, can't see otherwise).

What do you call crappy mileage? I get about 25mpg when I drive like an idiot My '99 NA topped out @ 42mpg on 0% ethanol (f*cking government) back when I had it, could drive from Miami to Nashville and only needed to fill up once in Georgia w/ ~600 miles per tank. Regardless, a bad O2 will affect your mpg, but isn't going to cause any issues. My EGR is blocked off tho (I will get poorer mpg).

'Off-boost' throttle response during vacuum won't be as zippy if you're trying to compare a low-compression engine w/ very little backpressure, to a NA. If you're trying to make up for the low end, the most you can do is a lightened flywheel/etc to push up the rpm's quicker. Is your air filter clean? lol, had to ask :p

What size turbo do you have, and how much lag is there? My S16G kicked in @ ~2500rpm if memory serves and was good up to about 5500rpm before power leveling off. My S20G-H kicks in @ ~3500rpm and is good all the way to redline. The tradeoff is the extra power compared to low lag. If I'm cruising, I'm in vacuum... if I'm moving, I'm in boost.

I reran a lot of fuel lines 1~2 years ago and sent my injectors in to VAC? (I forget the name now, injector cleaning place) because I've been running on them for 5~6 years now, and they tested in perfect condition. I'm inclined to think it's not an injector issue.

Sounds to me like your computer is playing games with you... I have a Hallman MBC, so not sure what you're doing to manipulate the MAP voltage. Because I have a SAFC wired in, I can easily check the voltage of the MAP @ the sensor and directly only the computer both, maybe checking it out would help. I've gotten bad MAP sensors before, and wouldn't rule it out... and check the wiring to make sure that's what the computer really is seeing.

I bought a Symtech FCD way back when, even stopped by Paul's house and let him hook it up (so I wouldn't screw it up, lol). But I eventually lost patience with adjusting it, couldn't get it quite right, and went back to a Missing Link.

- J