I started up my car today and it made a really odd noise. It wasn't like a knocking, maybe a slight clanking noise, but more like a swirly shakey noise. And then I opened my hood to listen carefully, but I did hear anything coming from the top half of the engine so I took the oil cap off while the engine was running. Now I may be an idiot and not have known this would happen, but when I removed the engine oil cap, the whole engine shuttered, so I quickly put the oil cap back on and it was fine. Does that indicate a problem, or is that normal for this engine? All this is added upon the original problem of the idle speed dropping to 500 then to 1000 then to 500 and finally to 750 after I came out of gear to drift. I have an appointment for friday, and I'm terrified that I'm gonna get horrible news of a piston broken or a valve fell out or something. I guess I should have prefaced all of this with the fact that my engine went into the red zone for about a second (6500rpms). I'm assuming this current problem is due to my stupidity. If any one can rest my fear that I'm gonna get really bad news please tell me. Also I haven't changed the oxygen sensor yet, and I got 112k on it.