I have a question on a vacuum leak issue. I have replaced the UIM and LIM, a new PCV valve and MAP sensor and there is a slight hissing sound coming from the engine now. I have read other posts and I do have all the o-rings replaced and all is snug. Now I was looking at the illustration in my service manual and it appears that there is a spring in the PCV housing. I did not notice a spring from the old original UIM and did not recieve one with my new one from APN, is this spring necessary? I let the car idle and removed the oil fill cap and it almost stalled but recoups and continues to run. I read B. Buttermore'* post on a vacuum issue : (We had an L27 with a nasty vacuum leak to the crankcase caused by failed LIM gaskets - I don't doubt that the L36 could do the same.) I just changed the LIM gaskets and sealed them pretty good w/ silocone whats the probability there is a leak and if so how can I locate it ?