The oil trap is just under the flame trap. They do plug. Cost is about 30-35 from Volvo. Some folks clean them. Be sure to get a new O ring for it. Two bolts hold it to the engine block, approx under # 3 intake manifold runner. a little frustrating to change, but not that bad. Clean the area around it before removing so dirt doesn't fall in. Also, check all your vacuum connetions on the manifold---these plug up. Cleaned mine by using coat hangers etc to get a better flow.

Hope this helps,

dick