I have just bought a 92 sri 16v......the owner had just had a head gasket put in but was ****ed off with thee car cos it still wasn't running right. Engins sounds fine and goes well but at tickover it 'hunts'. The revs go up and down somewhere between 500 and 1000. This happens when the engine is cold and when it's hot. All the hoses seem ok...any ideas please?