If you remove the spark plugs that will take all the pressure out of the cylinders.As far as air lock,just air shouldn't lock up the engine,I would think it would be water of fuel.Check the cylinders when you remove the plugs.If one is full of water or coolant you might have a cracked head of blown head gasket.Depending on year and engine size,cracked heads are common(I've had one,1985 1.9L).If one if full of fuel then that fuel injector might be stuck open.Hope this helps(and itn't to depressing).
chris
January 2008
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