Was the turbo new when he bought it? Is there any smoke? If nothing is showing on the wideband then more than likely it is not an A/F problem. Pull the intercooler piping apart and check to see if there is any oil in the pipes. Check the plugs and see if they have any oil residue on them. If not check the TPS like has already been stated. Sounds like you are having an ignition issue to me though. Although the coil pack seems fine, under a load like part throttle pulling up a hill your coilpack can start to break up but not that often. Most I've seen either work or not. I'm just trying to give you a few easy things to check first.