Hi All - Please help :(

I bought a 320i BMW. After like one drive, the brakes went stiff and really hard to press. I assume brake booster and the vacuum etc. before I could get to a mechanic, the car started shuddering and like revs were below 900 and going up and down, so I took it somewhere decent and they diagnosed it, and changed a coilpack as well as my spark plugs. This seemed to fix the shuddering/revs/limp mode situation. I went and took the car to a brake specialist, they took a few days and replaced my vacuum pump and fixed my brake booster. When I went to fetch the car they said it is in limp mode. When I started the car, it definitely is doing the same thing in terms of the shudder or limp mode as they say. There are no errors on my dash, and they advised no error shows on diagnostics and my brakes work fine now. They said it isnt anything related to the brakes.

I have no idea how to proceed? is it something they could have caused? or could it be my other coilpacks or could it just one problem after the next?

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What should be my first step? how do I manage these brake specialists?

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Please help, Iv already spent so much money to sort these things out and im stressing.