[CSCUK]

Hi.
Help needed to diagnose fuel starvation fault on 1999 v70 2.5 petrol.

Fault description:
Starts from cold first turn of key.
Engine revs normally when I press the accelerator until engine hot.
Once engine has reached normal operating temperature if I attempt to rev the engine it dies immediately then will not start again until cold, once cold again engine will start and rev normally again.

I have renewed the fuel filter but it has made no difference whatsoever.

Back story of pattern of use of the vehicle prior to fault starting.
(this may give a clue to what is wrong)
I only use the v70 from June to late autumn as a surf wagon which I live in at whatever beach I'm surfing.
Between late autumn and June I take it off the road. Every June it starts first turn of key and then drives hundreds of miles to beaches without any issues.
Same story June 2023.

First occurrence of fault.
After being parked for a month at a beach I did a routine start and ran the engine until hot.
When hot I tried to rev the engine and it immediately died, although it stayed running (just) and each time I tried to rev it would almost completely die, but just manage to keep ticking over.

To fix this I used fuel system cleaner and poured the bottle into the tank before starting from cold.
When it reached normal operating temperature I very slowly pressed the accelerator to try to rev it (I'd already discovered that if I pressed fast it immediately died)
The slow pressing of the accelerator gradually increased the revs to higher revs without it dying, so I did this repeatedly until it was revving higher and higher.

Then I tried pressing the accelerator fast.
It revved without dying, but with a distinct pause between the press of the accelerator and revving, like it initially missed firing and then caught up and revved.
I continued revving it in this way until the fuel starvation completely cleared and it started revving completely normally again, no matter how fast I hit the pedal!
So I think cool, fault fixed, I can continue rolling.

Fast forward to late autumn and another beach.
It's now a month from when I had arrived at this beach, hoping to ride the majestic waves rolling in from the deep ocean swells off the coast of Africa.
Seriously awesome rides.

I do a monthly routine start and it was back to the exact same fault of dying once hot (despite it still having the fuel system cleaner in the tank!)

I walk into the local village and ask a mechanic at a garage what he thinks. The mechanic says it sounds like a blocked fuel filter. He says it may have gone worse coz of the fuel thickening over the months the car wasn't used. He says the 95 octane e10 fuel has a tendency to thicken with age.

I jump on a bus and get to a bigger village with a garage that sells 99 octane fuel. I fill a fuel can and take it back to my fuel-starved surf wagon.
I tank the 99 octane, start it cold then slowly rev it until the fuel starvation fault completely clears (exactly as it had done when I used the fuel system cleaner to clear it!)

Going by this, I only needed to have bought 99 octane fuel and not fuel system cleaner. Although the fuel system cleaner was still on board so could have helped?

Once it's revving normally I drive to a garage and fill the tank with 99 octane.
I then drive hundreds of miles stopping for varying lengths of time, (but never longer then two days) after all stops the wagon starts first time without fail, whether starting from cold or starting from hot.

It's now late late autumn and the nights are lasting 14 hours.
It's time to begin the journey home.

Certain that the fuel starvation fault is 100% fixed I drive the 300+ miles home (starting the wagon from hot a few times along the way without any stalling or dying)
It revs and performs perfectly the whole drive home.

Arrive home late autumn and park the wagon. Disconnect battery.

Last week I attempted a routine start and it's fuel starvation fault is back, and if anything it's worse than at the beach, because now it dies completely when revved instead of dying but still ticking over (albeit only just) like at the beach.
I thought changing the fuel filter would have fixed this but it has made no difference at all.

Yes, the fuel starvation fault can be temporarily fixed by slowly revving the engine until it builds up to higher revs for long enough to clear the fuel starvation (as I've described doing on two successive occasions)
but there must be something mechanically wrong for this fuel starvation to keep reoccurring.

I have previously left the wagon unstarted for long periods of time without it ever causing this fuel starvation problem,
including an 8 month period after which the wagon started and revved normally when hot, after not having been started for 8 months!

Appreciate help in identifying cause of this fuel starvation caused, or worsened, by leaving vehicle unstarted for long periods.

KRS