when i accelerate there is a big loss of power,it sounds throaty, it idles ok

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it is ongoing all the time on acceleration attempts, drives like a slug, even worse attempting any hill climb having to drop back a gear to even just make hilltop. I have had a air flow meter and purge valve replaced after a diagnostic with no cure, I have put new spark plugs in also. It makes a deep throaty noise revving up and during acceleration . I noticed today whilst i revved in driveway that it sounded deep throaty noise but during a bit more higher revs it sounded spluttery and sort of tinny sparking noise. best way i could describe it sorry.Hope you can help please as Ive stumped 2 mechanics who helped free of charge.