With access to under the timing chain cover and the gear for the vacuum pump, can you determine if the pump could be making an awful knocking noise. Or if you pull it, can you check it on the bench. I am already to the point of being ready to pull head bolts, but if I can determine that the pump is the colprit, then I don;t want to pull the head, yet hate to put it all back together to find out that the pump didn't fix it!

Any help would be greatly appreciated, planning to work on it more today.

Thanks