So maybe the throttle plate should be "helped" with a rubber cap on top of it. The pressure on my hookup never exceeded 3.5 PSI. I would want at least 15.
First, I forgot to explain that even after I reversed the valve I was talking about earlier, there still was a buzz when I was pressurizing, only with a different pitch. So, either the valve is just not working right anymore, or it's normal.
Second, as I was pressurizing, the pressure did not go up past 3 PSI, but when I would release the compressor chuck the tire valve would hold 3.5 PSI for a while. I could even walk to the trunk, bring the tire gauge, come back and still measure 3.5. It's just that there was no way to go up in pressure, almost like something was venting (nowhere visible) as fast as the tire compressor could pump in and was stopping venting at 3.5. I was spraying soapy water all the time.
One thing I heard and believe might be true, is that all motors stop in the same respective position, every time. A mechanic once pressed out the starter toothed crown off the fly wheel, because it had a dammaged sector and then re-pressed it at a different position of the bad sector and that took care of the problem.
If this is true you will, for example in a 6 cylinder have the engine stop in such way where a pressure test is possible, because valves are closed, while a 4 cylinder always stops with valves open. What do you guys think?