i recenmtly had a 500 efi rebuilt problem supposedly was that engine took in water thru the exhausts. rusted and broken valve. now engine stalls at low speed and runs rough. any ideas

Valve adjustment too tight, timing, IAC ?????

Maybe water getting to cylinder from exhaust did you fix or replace the exhaust.

I would start by checking the base timing and that the Iac is opening and working properly. You did fix the water problem??