Terrios idles too high

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Hi, can anyone help. I've a 2007 terrios 1.5 that idles constantly at 1500 rpm. The only way it'll drop is by taking the vacuum off the MAP (already replaced) but then of course emissions and smooth running are way off.
There are no issues with the accelerator cable movement. At idle the throttle position sensor is reading 12 and although I can undo it and rotate it to read low the engine then stutters to rev.
Strangely when the car is idling at 1500, if I blip the throttle it responds immediately then drop back properly for a split second before it jerks back up to 1500.