A lot of people on here use the teflon gaskets and most have good success. However, I know from past experience that this is not always the case which is why I mentioned that they can cause issues. I did not go into detail on any recommended solution, but the rubber 0-rings is not the right solution. I did recommend a smoke test to see if and where you might have leaks. There are many places that an SC intake system can leak, in fact they are too numerous to list. I recommend you put the teflon gaskets back in and then have it smoke tested. This will definitively locate any possible leaks.
I still don't know what year your car is or if it has EGR, but a sticking EGR valve can definitely cause idle issues too, so don't overlook that.
Stock idle speed is 550rpm in drive and 700rpm in neutral and our tach's are notoriously inaccurate, but in any case it should not be shaking so it seems clear that something is not quite right.