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Diesel?
The odd bubble going into the pump isn't anything to worry about, but a constant stream of big bubbles will undoubtedly cause bad running.
I'd be looking for air getting into the system...

It'll have a recirc valve, same sort of thing, but instead of venting to atmosphere, it vents back into the intake manifold.

In defence of terraclean, it doesn't claim to be able to help in situations like that.
I don't like to say this, but maybe the garage is struggling to diagnose the issue and did a terraclean more...

Already said in post #3.

I got a 4 piece set off ebay for my V50. They were 30-35 quid. Top quality

Sounds like you may have a Vac leak. That will make your throttle erratic sometimes.

No idea,

Some shops sell 4 piece ones but I don't think that's what you're after... ;)