Poor Running between 1000-3000 rpm

Picked up a 96 1.0 K11 a few months ago as a cheap runaround, it has an annoying little fault which I'm trying to get to the bottom of, hopefully you can help!

Basically, when started from stone cold it'll go like a rocket with no problems at all. But soon after that, problems start. Once the engine starts to warm up it will feel a little lumpy between 1000-3000 rpm - a few jerks as you accelerate through this range then the problem is gone over 3000 rpm or so and it runs fine. Once the car has warmed up properly this problem gets worse, the engine really struggles and feels like it's missing/mix is wrong, but again not below 1000rpm and not above 3000.

It will always start first time, it idles fine and will run without missing a beat once above 3000rpm, the problem only happens in that specific range. So it's difficult to drive 2 miles through town to the shops (or I go around in low gears to keep the revs up but look like an idiot doing so) but yet it will happily do a couple of hundred miles on the motorway without any problems. It also doesn't seem to be getting any worse with time, it's just annoying.

Plugs, leads and air filter all look OK (although I haven't replaced them), I'm leaning more towards throttle body, I've read a few similar stories, but not quite like the problem I've got.

Any ideas?
 
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