Remove and thoroughly clean the throttle body and idle control valve.
Re-assemble using new gaskets.
Throttle body aerosol spray cleaner approx £5 from halfords, work it in with an old toothbrush.
Gaskets about £9 from Vauxhall dealer spares dept.
Sometimes the idle control valve has to be renewed, cleaning may give only a short term fix.
vaux
February 2011