General Possible ECU or MAS problem

[AndreMP]

Hello, I'm a proud owner of a 2g dsm 4G63 N/A in Portugal but currently, my happiness levels have been decreasing... Here's the scenario: The car is stock (except for the exhaust which has no catalytic converter anymore) and under full throttle, it stutters around 4.5k rpm (it gives the impression that the car is running lean). Since the MAS was old (original Mitsubishi part with number E5T06071), I proceeded with it's replacement, getting an aftermarket variant (from Herth + Buss), which was compatible with my car. So, after installing it, the car runs rich, having a sluggish like acceleration until 3k rpms (no matter the throttle position) and after (at full throttle), keeps on accelerating but on a lower rate than it would with the MAS unplugged. Moreover, with the MAS unplugged it runs great when it is at 194 ºF (normal running temp).

Any ideas around?