Ford Focus 2.0tdci 2005 - Engine suddenly lacking power / noises

have the engine mounts checked as they may have failed and the rubber is no longer insulating the engine and transmission from the cabin.

Is it low on fluid?

I have same car, some rattling engine noise especially at low revs, engine light came on, some loss of power, dealer plugged it into computer, said it was the belts/chains for variable cam system, I got them replaced (there are 2 of them) and now its good.

Passenger compartment fuse panel
The fuse panel is located below and to the left of the steering wheel by
the brake pedal. Remove the CD stowage box to access the fuses.
To remove a fuse, use the fuse puller tool provided on the power
distribution box cover located in the engine compartment.

Power distribution box
The power distribution box is located in the engine compartment. The
power distribution box contains high-current fuses that protect your
vehicle’s main electrical systems from overloads.

For this and other details can check the 2005 Ford Focus - Owners Manual (page 148 and next).

Hope help with this (remember rated this help). Good luck.

These are common for a lifter noise, the problem is the lifter. They get dirt in them and sometimes dont recover

Power Steering will make a bunch of noise when it is low on fluid. Find the spot it is leaking from and fix it, then make sure the fluid level is at full then you are done.

Continuing to let the power steering stay low on fluid can cause the unit to fail.

Maybe a stray leaf, twig or other small object has been sucked into the ventilation duct, touching the centrifugal fan.
You need to pull off ducts around fan and inspect.

Taking a look at your plugs can tell you alot, check spark,timing and fuel. It can be many things.

the grinding noise you hear is the pump out of fluid you need to find and repair the leak then check the pump it may be u/s if no oil in it and it has been run

you have a power steering leak, when in full lock position the power steering pump is actually sucking in air and this is your noise. you will have to locate the leak and replace the leaking part and fill it to proper level.Ford will accept trans fluid for power steering fluid.