Give all your electric connectors a check. I had something very similar, but a bit further up the rev range. A well reputed specialist had no luck, eventually the engineer in me took everything back to basic principles. It was water in an engine loom connector. Admittedly under one of the blanked off vents on a Classic, but there are still other ways in on a newage.

The TPS was replaced two weeks ago, and the behaviour was the same before and after the change.

Can anyone recommend any good specialists in the South East (Guildford to be precise)?

Haven't used them yet but Surrey Subaru Specialists have a good reputation. Think its LegacyDan on here? Otherwise Len at Subaru4You if you go as far as Newbury.

Thanks, I'll give Surrey Subaru Specialists a go.

Did you check the throttle movement, have someone watch the butterfly as you press the peddal down slowly, see if movement is smooth...that will check both the cable and the butterfly movement in one go.

Just got back from Surrey Subaru Specialists. This has foxed them too.The only thing they could suggest would be to replace the IACV. As it is a tad pricey from Subaru, does anyone have any suggestions wher I could source one from as I'm not sure it will fix the problem. I've given Grade A a call but they don't have any in stock.

Thanks.