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If your o2 voltage keeps raising with RPM and Boost, then your scaler is too high. I have done tons and tons of tuning with my 8 injector setup both on the road and on the dyno, and I'll add a few things that I have seen with my setup. First off, I have my map cut rate set at its absolute highest setting (like 255 or close to that) and have no restrictors in the dedicated vacuum line running to the 034EIC. The way I see it, you want the 034EIC running as close to real-time as possible to adapt to rapid changes in boost immediately. I ran the car this way for about 2 weeks with good results before I pulled the motor a few weeks ago (replacing tranny input shaft seal, adding cams, and more goodies  ).
I also ran into the hesitation at 0 psi, but it was strange what happened to me. In my case, as soon as the car saw 0 vac, it went totally lean. Every time my a/f gauge would read red and my car would bog and backfire out the intake (i could hear the BOV from it) so I know it was lean. This didn't happen immediately after setting up the 034EIC. In fact, this happened about a week after I tuned on the dyno and had all of my numbers reading almost perfectly. The only thing that I can guess that caused this is that during partial throttle boosting, all of the added fuel tricks the stock ecu into creating a leaned out fuel map at 0 vac. Since the computer thinks the car is at 0 vac when you are boosting, it compensates for the excess fuel delivered during partial throttle boost, thus causing a lean spot when your car is actually at 0 vac and the 034EIC isnt adding fuel. I compensated for this by having it start squirting fuel at 92 KPA, and altering the matrix at that pressure so that it squirted less fuel than it does during boost (I began the line with 0.88 and finished at 7000 rpms at 0.96). By doing this, it completely eliminated the hesitation and made my transition into boost flawless. I would be willing to bet that those of you who are having a hesitation at 0 vac are having this same problem. When it hesitates, watch your a/f gauge closely and I'll bet the voltage stays lean (even in closed loop mode).
I would think that another way to correct this problem would be to lean out on the 034EIC. My guess is that during partial throttle boosting, I am running so rich that my primary injectors are barely needed to provide the proper amount of fuel. Because of that, the stock computer learns to squirt less fuel when the car reaches 0 vac. Now, if I were to lean out the 034EIC so that the stock injectors were still dispensing fuel at the same rate as they would at 0 vac, then you would have no lean spot in the transition from vac to boost. I will try to do this better once I have my car back and running soon, but trying to get accurate fuel trim readings at 15 psi of partial throttle boost is nearly impossible. And, even if I do get the numbers dead on in the 034EIC, I wouldnt know it for a long time since it takes the computer awhile to compensate for those changes. I definately think that squirting fuel in vacuum is an easier and safe fix, but probably not best for performance. Although, honestly I dont care about performance at 0 vac much anymore  . Matt
1995 Eclipse GS
2.0L, S16g Turbo, 8 Injectors, 26psi
1998 Eclipse GSX
2.3L Stroker, AEM EMS Converted to Speed Density, FP3065 Turbo, 35psi , and so on...
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