Tachometer moving erratically, drives like it is in limp mode

At first I was getting error 54 on the internal dash display which means water in the fuel filter. Then I started to notice that the idling revs were jumping all over the place. I was getting a P2282 error code on the OBD scanner. This helped identify that the intercooler hose had a split.
I changed the intercooler hose, and the revs issue has stopped.
I changed the fuel filter three times, and still get the error 54 on the internal dash display.
Also, the car has no power/boost. It drives like in limp mode.
There is no engine light on other than the service car light, which I presume is because of the fuel filter message.
When I got a mechanic to plug in a reader the only thing that came up was that glow plug 1 needed to be changed.
Can anyone please help me out with this? I am at my whits end.
I have already cleaned the EGR, replaced the MAF sensor, replaced the fuel pressure sensor on the rail, and cleaned the MAP sensor. The intercoolder hose has been changed for a new hose, and I have put three new fuel filters into the car over the past four weeks.
No error codes reading. Mechanic is not using cheap equipment to perform diagnostics.
I just cannot understand what the problem is.
Could the turbo be the problem, or the boost sensor?
Surely this would throw out an error code, wouldn't it?