That screw is called the throttle stop.
It’s purpose is to stop the throttle blade when you let off the accelerator.
It’s not for adjusting the idle.*
To me, it sounds like you have the timing incorrect. But you also have a MAF code, so start there.
Is this a new issue after you did some work? Or was it like this when you acquired the car?
87 coupe 5.0EFI conversion, SN95 5lug,
95 GT, V1$-Trim, NoSlow5.0's Motorsports intake, TwEECer RT & etc...
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