2003 Toyota Prius, almost 100k miles, has run great up until now. About a month ago I had a violent engine shake for a few seconds upon a cold start and then disappeared on it’s own. I’ve read this is a common thing with some Prius during cold weather so I chalked it up as that…but still somewhat concerned. Now, on cold start it runs smooth for the first two seconds at normal idle, it then goes to a slightly higher rpm idle and it’s common movement/feeling of going “into gear” (which all seems normal for a cold start hybrid). It then begins a random “misfiring” feeling. As the engine gets warmer the “misfire” is more frequent and pronounced (same feeling as a month ago) until I turn it off because of not wanting to destroy anything. I’ve run it with the whole air box unit disconnected from the throttle body once and it seems to run (high idle) without misfiring until it shuts down due to (what I’m guessing is) the MAF sensor getting a misreading as it was disconnected and not in-line with the incoming air. I’ve changed the plugs, cleaned the throttle body, and installed a new MAF sensor but the problem still persists. Taking a look through the throttle body and into the intake manifold it’s dry (no oil, etc). If it was an injector would it idle properly for the first few seconds? I don’t think it’s a coil and my guess is a sensor but I’m not the mechanic. Is it vacuum? EGR? TPS? I’ve also read there is a design flaw on the cam gear for newer gen Prius. Could that be an issue for the ’03? No CEL light but I’m sure I would get one to come up if I let it progress into the terrible engine/”misfire” noise. Not something I really want to do and I would imagine I would only get some sort of a misfire code which wouldn’t really help. Any ideas? Any common Prius problems?