From what you say there has to be there has to be something different about the formulation of the two fuels.

It sounds like it could be the old problem of supermarkets selling fuel at the end of it's storage life rearing it's head again.

It happened to me once with a motorcycle, having filled with supermarket fuel, misfiring, wouldn't idle properly, got some fresh UL98 into the tank, back to normal.

Read here about what happens to petrol when it's stored:-

chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://www.bp.com/content/dam/bp-country/en_au/products-services/fuels/opal-fuel/Opal-factsheet-storagehandling.pdf

"it could be a high water content due to condensation in the filling station tank"

But you said supermarkets have fresher fuel by virtue of their high throughput......?

I have a busy garage near me (ie petrol stock changed frequently) that my Superb hates (I won't name and shame though) - it's lumpy and hesitant with it. I simply avoid fuelling up there.

My Superb runs really well on Tesco Momentum so I generally fill up with this ( I have a few Tesco petrol stations around the country logged into my satnav!)

Edited by Big John on 07/04/2019 at 01:13