So I bought a wrx a little bit ago and it ran fine when I checked it out. It’s an 03, has a catless downpipe, 3 inch exhaust, and typhoon intake. Previous owner said it was tuned at one point. Obviously I couldn’t trust that and have not been driving it hard in fear of running lean, However, I notice a slight surge/hesitation around 5k rpms, so I pulled the maf sensor, cleaned it and put it back on. Now, it runs awful. If you slowly get into it you can rev it out, but if you get on it, it will feel like you hit a wall around 5k, and boost will be around 6 psi. Could my maf sensor be bad? If not, what could it be? Maybe a boost leak? Is there any way to figure out if the maf is bad before buying another one?