hi there,firstly try cleaning the idle valve before you do anything else and see how that goes.if that doesnt work let me know.by the the idle valve is located under the inlet manifold which needs to come off.it wont be the throttle position sensor.
do you have an aftermarket headset?
i had the exact same problem with the rattling noise and approx 3000rpm in any gear and after a painstaking search i realised the CD spinning inside the headset was vibrating and making the noise...hope it helps
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