Volvo Penta D2-55 hunting at idle

[RRuhge]

Hello.
My D2-55 is hunting at idle. That is, it does not keep a smooth idle. It slows, shakes too almost stalling and then speeds up. It cycles through this in a 2-second interval. I spoke with the local Volvo shop just as they closed the shop. They seemed very familiar with those symptoms and said I need "Pump service." Okay, I presume it's the fuel pump.

Does that sound right? Is that a high pressure fuel pump? or the pump prior to the fuel filter? How expensive will this be?
Rob