500hp efi/whipple
 

port motor stall when put in gear mercury diagnostic show no fault on anything including IAC hit throttle quick it will stay running idles fine in neutral only does it in water not while on flushing device when prop is out of water any ideas?

With scan tool connected, go to TPS voltage setting in idle and adjust Whipple throttle stop adjustment so that the TPS voltage at idle is approximatly 0.65 volts at idle. If this voltage is to low the computer will adjust the idle rpms to low for idling in gear and the engine can stall. This may or may not be your issue.

Best Regards,
Ray @ Raylar

Check the IAC filter. If they get dirty the Whipple engines will not idle properly.

i will check both things thanks