You need a new pair of scissors, that cutting out is appalling. S'all wiggly. Were you doing it while driving?

Good, now time to find a new garage.

If its a diesel it could be the EGR valve is sooted up. YOu can change them easily and get cheap reconditioned ones from Ebay. I had to do it 4 times on my Alfa (yes its was an Alfa and yes the electronics were dodgy). The best buy for me was the ECU cable and some free software to help diagnose without going to the garage first.
 

My missus's old Fabia had that. Started intermittently and got worse. Garage checked it and said that the engine temperature sensor had failed. Not a big or expensive job to replace it apparently.

IME, that's usually a lambda sensor fault, which would also fit in with most of the other issues you've described. A fault code check would confirm, it's an easy fix but usually needs a specialist tool 

code check first though

Never had to do a lambda sensor, but presumably a crows foot would also be fine? Or do you need the extra vertical grip length of a socket for those buggers?

Fucking hell. I'm glad my service garage engineers only speak German and I don't.

a crows foot might work, they are usually rusted in pretty good

Hah, what isn't?

I had the engine light come on in a rental on the 3rd day of a 1-week rental (it was a newish, low-Km car). I phoned the rental company, and they told me to ignore it.

Uh oh, I said "rental" three times...

It's autistic.