Yeah did that when swapping plugs, all pressures normal. I was going to do my head gasket if low, or I saw a clean piston, everything looked good though. I was hesitant to pull the head, I havent done one on a prius. Figured it would take me a couple days.
Sorry if this is a lousy question, did you open the throttle body flap when you were cleaning it? Check the butterfly flap to make sure it is not out of position. Also, try using hybrid assistant. Instead of doing things randomly, this can monitor all the related temps including MG1 & MG2. So you will know if it is temp issue or not.