I wouldn't bother with the timing chain, it is probably unrelated to this
problem.
What I would look at is a vacuum leak like others have suggested. Pinch the
PCV hose and see if the idle dips a tiny bit, if it does its okay. If the
RPM rises, you have yourself a leak so start sniffing for one. If the idle
still fluctuates, try disconnecting IAC valve and see if the idle settles
down. Let us know how its going.
Ken
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