Need help again :(

[Adam 180 V6]

Hi i recently posted on here about my cars random revving and holding the revs and cutting out etc.

I scanned the car and it came up as a Throttle position sensor. So i replaced the sensor and also idel valve thing thats located on top of the throttle body housing.

The random revving on tick over has now gone and it doesnt stall and no fault codes have came up, Although its still ticking over too high and when driving along at 3k or 4 for example when i lift of the accelarator the revs stay where they are untill i put into a lower gear so its like holding the revs at 4k when in neutral. I have noticed when i accelarate theres sometimes a hissing noise, im just wondering if maybe i have an air leak??

Any help on diagnosing and fixing would be appreciated.