Hi,
It sounds like one of the belt-driven accessories is failing.
The Fiesta wasn't offered in the US in 2005, so there are no listings in my manuals. However, the first thing I would suggest is to remove the accessory drive belt or belts. Spin each of the components and see if there is any excessive resistance. Also, see if there is excessive play in any of them.
I found a pic online, but It's for a 2001. It should be similar if the engine is the same size. Note there is a belt tensioner and an idler pulley (numbers 2 and 3 in the pic below). My first suspect would be that one of them is failing. Remove the belt and see if any of the driven pulleys seem bad.
Let me know what you find.
Joe
See pic below.
Image (Click to make bigger)
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Saturday, June 25th, 2022 AT 9:52 PM