Volvo Repair: Check Engine Light, intake manifold gasket, head gasket

Question
1995 850 Turbo Automatic
My Check engine light keeps lighting up. Each time i take it in they tell me the fuel mixture is runnng lean and then they reset it. What is the problem that can be causing that and is it possible for me to reset the light myself and not pay them $60 to do it.
I was told by the lube shop I have water in my oil. What can cause that and what problems will it cause me, can I do anything to fix it?
Thank you for your help.
Mike

Answer
the lean running could be many things.most common would be a bad vacuum hose or the intake manifold gasket is leaking.as for the water in the oil this could  be caused  from a bad head gasket or crack in the head.I would have it looked at by the dealer or a good mechanic familiar with volvos.