The PCM will detect a leak about 1/20 of an inch, on 2000 and newer it is 1/40 of an inch. So the leak your looking for could be that small.
Secondly I had PO171 on a Zetec though and it was my injector O rings, finally found out they were leaking replaced them, problem was fixed.
The O rings would leak air on the intake stroke, creating a vacuum leak, causing the CEL.
So you have sprayed all around the gaskets, and the RPMs didnt change anytime at all, if they did change at all there is your leak.
