| If you haven’t been using Shell V-Power already, stick a tank in along with some fuel additive.
Cant comment on which additive is better as they all claim to be, so just go for a good make and one that you put the whole bottle into a full tank, otherwise you have to keep fannying about adding a bit each time you fill up.
The additive will clean out your injectors and fuel lines and any deposits in the engine. V-Power has additives already in, so it will keep everything clean once you have used the additive.
I always use V-Power and used Optimax before it, all my cars have run much smoother and gained a few bhp, especially previous turbos and now the supercharger.
I appreciate that it is more expensive to fill up on V-Power but I do so little miles that I don’t mind, if you are doing high mileage than perhaps fill up every other tank and use good quality normal unleaded such as Shell in-between.
To cut a long story short I work in the oil & gas industry and Shell’s petrol is amongst the best and their V-Power has won loads of tests by EVO magazine.
This will hopefully sort everything out, but if you fancy a little cheap DIY maintenance then stick in a new uprated panel filter, and better spark-plugs, both are inexpensive and easy to fit so why not.  | 
