Chevy Cobalt LT 2.2 RPM Bounce Issue

I have a 2009 chevy cobalt lt 2.2 litre engine. It has many mods that were not
done by me, I'm the second owner. It has 105000km. It has a supercharger,
coolant for the supercharger, some gauges that aren't hooked up, fully
custom exhaust. It was essentially modded to be a Cobalt SS. The problem
that I'm having has been going on for some time now. Whenever I'm driving
and depress the clutch fully to make it go into an idle state, at first the RPM
will bounce down to around 500-600 rpm and come back up to its normal
idle(around 750-900). Sometimes itll bounce around in the 500-800 range
and come back to normal. When this happens i can audibly hear the change
in sound from the exhaust, sounds like its close to stalling. I've tried cleaning
the throttle body, even completely replaced it, changed plugs and just some
general cleaning around the engine bay. I don't think there's any vacuum
leaks. Nothing noticeable anyway. When just idling the car runs completely
fine, it's only when i depress the clutch completely when coming to a stop
sign or something that it bounces around. It appears that it's getting worse,
only thing i can think of is that it might have a bad o2 sensor. both the o2
sensors are pretty jumpy as far as readings go, im not sure what they're
exactly supposed to read anyway. Could also possibly be MAF sensor
related. Thanks