You have a stock Mustang GT pump or an upgraded? I hope it was upgraded...stock is small as hell.

Is it a violent buck...like the type that makes you think you broke something or just a slight stutter? If its a very violent buck then its fuel cut...otherwise MAF overrun or a boost leak (which I forgot to mention).

Either way hacking the MAS will drop the Karman counts and consiquently lean out the engine...which *SHOULD* cure the MAF overrun as well as the fuel cut. Just make sure you dont end up running the engine too lean (might want to verify what pump you have).

I ran my 1G MAS with the center honeycomb *ONLY* for quite a while without any fuel control and I didnt run into fuel cut until I added the AFC and bumped my fuel trims up (which in part defeated the purpose of hacking the MAF...but it still wouldnt hit MAF overrun).

You may also have a boost leak. It would cause the symptoms you are describing. Car should go VERY rich if thats the case. Normally I see .84 or so on my A/F (90s are lower O2 voltages than any other year for some reason) and when I got a boost leak at high boost the A/F gauge would practically bury itself at 1.00V.