Remove and clean the throttle body and idle control valve. Use new gaskets when refitting.
This is usually just a short term fix, if the problem comes back you will need a new idle control valve.They are not too expensive.
Copy and paste-
http://www.autovaux.co.uk/LoadPortal.aspx?cnum=47&pnum=AS90411546&tabid=5&vnum=136
for example.
danda
March 2011