The throttle blade is probably sticking on the intake plenum. Considering its only about 65 or so mm compared to the 75mm TB... and this can actually hurt performance. The MAF would have been a good place to start, and upgrade the TB once you have a bigger intake plenum installed.
If your sticking with stock injectors, and going to the bigger MAF you'll be alright because your not really going to see a big increase of air flow into the motor, until you upgrade the blower by porting or whatever... THEN you WILL need to look at bigger injectors, and that will land you the need for a chip.
As for leaning out, thats not really going to happen in your case with a stock blower. Now if you installed 42# injectors, and the correct sample tube for the MAF for those, and not run a chip, it will lean you out a bit, and screw up alot of other things including timing... not to good a place to be especially with boosted cars. Dave D wrote up an excellent article on exactly what happens with this process.