[Stl-986]

Very good question I think. This is something I have seen different answers on and different results, even with my 2 986's. Everyone says that if you take the cap off idle should change. Make sense. Some talk about how it should be difficult to take the cap off cause there should be a vacuum on it, but, there aren't many conversations about this.

With my 2000 taking the new cap off, idle changes and you can hear a slight vacuum noise. The pressure doesnt feel all that great, but that could be because it is a result of whatever issue this car has.

Now, with my 2003 doing the same thing the results are the same. Idle does change, and, that vacuum noise exists but it also doesn't sound or feel any different then my 2000 which clearly has an issue with vacuum or something not creating enough vacuum.

So to answer your question, no I dont notice much of a pressure, or a vacuum when removing the cap. With other cars like my Jeep Wrangler it works different. There is pressure when removing the cap and removing the cap is a way to tell if the rings are bad by causing blowback. Done this on many cars that I have looked at buying where you would take the cap off and see if oil shoots all over the hood. This is cause of course the cap is part of the valve cover, which in the case of a 986 isn't the case directly.

Really though, I am not sure if there should be pressure....or vacuum when removing the cap. Haven't seen anyone say one way or the other with certainty only that the idle changes.