Thats really weird that you would have back firing and no check engine lights! These cars are so sensitive that if you fart in the wrong position in your chair the check engine will light up.
Oil in the throttle body is very weird as well. Are you sure it's oil and if so how much? I think the best thing to do is have a friend put the ignition in the second position while you pay close attention to the engine and see where that clanking noise is coming from.
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