Loss Of Power And Then Not?

[mercenary]

Have a weird problem and not knowing much about motors im stuck.

I filled up yesterday at my local Jet station and since then ive had a problem.

When I accelerate all is fine until I hit 3,000rpm when it then starts to back off on the power, but then picks up again at 4,500rpm.

Could it be dodgey fuel or am I looking at something else? It sometimes stutters as its accelerating through 3,000 too.

Thanks

EDIT: Oh, and its only done 30,000 miles and just had a service in December.

[P38Aaron]

I had this with an older car, it was a crank shaft sensor...when it did that the misfire was constant at that rev range, i could drive round it no prob's at all.

But i have also had spark plugs do a similar thing.