Boosting Issues HELP!!!!

[Gandy]

Hi Guys.....
Sorry to bring up an old topic about my car ( Golf 1.8t 20v gti front mount intercooler, cold air feed, ARZ engine 2002 ) about my boosting issues....
Up until recently i've been having issues with my car accelerating as if its holding back a bit (Thats a nice way on saying its been acting like a complete dog). After I had some advise off you guys saying it might be the hot weather. Or a MAF problem which I checked and seems to be working fine, it was bugging me to find out if it was something else.
I notice recently that on the inside of my fuel cap someone has put a high octane notice to fill up at petrol stations. I had been putting in normal unleaded, but since noticing this I have changed to Shell Optimax and for some unknown reason the car is pulling much much better and is as it was before......GREAT I thought!!!
So the question I wanted to ask was.....................
1. Is this just a fluke and just coincidence that i'm putting in higher octane petrol or can you set these cars up to run on this fuel improving the cars performance?
2. If not, what else can it be?
Thanks for any feedback 

[baka]

Pretty sure the manual says 98RON fuel for the 1.8t.

For a turbo engine it's got quite a high compression ratio.

So I'd imagine using 95RON fuel in hot weather would make the engine hold back the timing.
 

[Gandy]

Its just funny that this is my second GTI and on the last one I used Unleaded only and had no issues. This one seems more fussy as there is a BIG difference in performance when using the different fuels. 

[Dalo Harkin]

It was probably mapped with high octane fuel, so anything less it wont be happy with, I must admit I switched from Shell to Tesco recently and every now and then I hit a pretty big flat spot (normally when pulling out at a roundabout or something) 
I might just switch back to Optimax again to see if it does the same

[Tezmax]

The fact you have FMI+cold air feed i would be slightly suspicious a change in 2 or 3 RON fuel would go from running like a dog to pulling as good as it ever did

But hey if it aint broke dont fix it

[Dalo Harkin]

It depends what it was mapped on, if it was mapped using higher octane fuel then it will make a difference

[Gandy]

Would you lot agree it might be an idea to get the car checked out. Would it be better putting it on a rolling road with a dyno or is there anything easier like plugging in VAGCOM or something to see what it is doing?

[Dalo Harkin]

Yes I would get it checked with VAGCOM, even a cheap ebay reader that can clear codes is a good investment when you own a MK4