more than likely your valve covers are leaking and when you pulled the plugs the oil just went down them
try cleaning them up and restarting the car
when you say the car doesn't rev well... does it surge when you try to gas it?
does the car smoke out the exhaust?
the temp sensor it is complaining about would be the ecu temp which is a green two pin plug on the side of the thermostat housing, check out the wires & plug and make sure they are fine
let us know how you go from there
