So here is my scenario.
The car is a 2006 Subaru Impreza 2.0 RS N/A, it has been feeling down on power for a while now and its not due to the lack of a turbo (well), it has been feeling down on power for a while its never been this bad.
I Filled up with Tesco monumentum, set off on a long 160 mile drive (mostly motorways) end up at ford fair (Yeah i know i don't know why either).
So i leave Ford Fair, but before i do i run an ECU wipe.
Don't notice any gains mainly because i'm not trying, i do another 80 miles mostly country roads after a 10+ miles on a motorway, i go to fill up with Shell V-power this time.
After 10 minutes or so i start to notice vast gains in power, which is strange.

Basically what i am dying to find out is the root cause of the gains, could it be the shell V-power although i'm pretty sure i have used in the past during the power loss period. or could it be the ECU wipe just before a long drive on a motorway? which has never been done before by me?

Any advice or suggestions would be greatly appreciated.
Cheers.

 

premium fuels use additives which contain things like injector cleaner, maybe something in the fuel cleaned something ? hard to say really

 

Placebo

 

I did consider it being a placebo, i have been there before.
A placebo would suggest that i was expecting gains.