My friend has a 1985 BMW 735i, a mechanic told him he needs a new fuel pump; but if you let the car sit about 10 mins it starts fine and just runs alittle rough..... Does anybody have any ideas what it might be?

 

not enough info.
It doesnt start at 1st then let it sit and it starts?

I dont know the 7 series. But most of the BMWs have a fuel pump in the tank and one under the car. It could be the one in the tank.

Also rough idle could be spark.. related.

 

if it hasn't been done in a while check the fuel filter