ST fast idle when warm

[Gaz w]

Bloody auto correct , the title shoud be fast idle

I've noticed that when the car gets warm it idles at about 1200-1500 rpm then slowly (after a while )drops to its normal idle speed
Any ideas as to why the idle is so fast when warm ?

[Simon T]

how long is 'a while'? For example, if I pull up to a junction and have to stop, mine idles at about 1200 for a second or so, then drops to 900.

[Gaz w]

About a minute or so. , when I first pull up it's at about 1700 then after a second it drops to about 1200-1500 then after a minute or so it drops to about 1000

[Ben Purnell]

edited the title for you

Mine behaves as per Simon above

[Simon T]

Something not quite right there then fella, air leak or maybe a sticking idle valve.

[robski]

Does it idle fast whilst coming off throttle whilst moving? Or is it stationary when this happens?

[Gaz w]

Does it idle fast whilst coming off throttle whilst moving? Or is it stationary when this happens?

Both , if I dip the clutch and let off the throttle at say 50mph it will be revving at about 1500rpm

[Simon T]

I think in that scenario it is supposed to idle slightly high, as the ECU is sensing that the car is moving, that is why the ST has a electric speed sensor in addition to the cable speedo drive.

[robski]

Disconnect the speedo sensor and see if the fault still persists
Also check the obvious, like TPS and if you have a dump valve they can play havoc with idling on a ST EScos