My car was revving as the OP had stated. I went through the usual test for vacuum leaks. No leaks. I then used the usual checks for pcv failure. I didn't notice the typical symptoms when checking for this. However, since the car had 155K miles and this could very likely be the original pcv or if not had not been replaced since I had it for over 70K miles, I decided to replace it. $180 is a lot better than blowing the rear main seal. It worked, now my RPMs are settling happily where they should.