Can anyone tell me what the tank below the expansion tank is. Its black plastic and has three connections. One is a tube to the throttle body, one is a sensor and the other goes to what I think is the fuel pressure regulator.

I think its a carbon filter but the problem is the sensor is making a fast clicking noise that I'm sure it shouldn't.

Can someone tell me what it is and why it's clicking. Probably FUBAR I guess.

Car is a Mk4 Golf GTi 1.8 20v Turbo 1999

Ta.

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swirl pot?

If it is a carbon canister then it would be to soak up hydrocarbon fumes which would normally come from the fuel tank whilst the car is sat around doing nada - By throttle body do you mean the the plenum intake valve (i.e an injected engine)? - If so then a bit of a mystery as no fuel here.

Is what you think is the fuel pressure regulator mounted to the top of the camcover? - This might be an expansion valve in which case you would get unburnt HCs that leak with other gases back up the valve stem seals.

Regardless - If it's making a din then bound to be fecked - Sorry can't be more help...

The carbon canister on my old MR2 used to buzz away to itself quite happily when the engine was off, I spent ages searching for an angry wasp in the engine bay until I eventually worked it out. Just because it's making noise doesn't necessarily mean it's berked

This is the same on my leon cupra and it seems the ticking is normal, well if its not mines being doing it for neigh on 4 years!