got a my03 wrx with ppp kit and a typhoon induction kit

my question is the car seems to a little sluggish from time to time and also i have noticed a slight pop from exhaust when you rev it then let it die off do you think it could be either of these.

 

just started car and took off maf sensor car went to cut out then picked up but at higher revs ?????

 

I think it should cut out afaik id keep an eye on that maybe try a mate's one in it see what happens.

 

pulled the maf sensor on my mate's buggeye and it did the same thing died for a sec and then picked up at slightly higher revs

bit lost wot to think now