If iDRAC is broken adding enterprise card will not help. You need to replace the express card. Can you try below steps and see whether it is making any difference
i have a poweredge r420, onboard idrac seems broken after last power cut (front LED not light up, POST take a very long time)   if i install a idrac enterprise card to it, will the server be fixed? (boot up as usual, without fan always full-speed running)
broken idrac