Hey damo when I rooted my EJ257... had similar symptoms as you.... car swallowed oil heaps. White/blueish smoke on start ups and sometimes whilst driving it would smoke.... backfired heaps. Felt a loss in power, idle was rough but not as bad as what you were saying. Mine just bounced up and down from 1k to 1.5k.

Hope you figure it out, what I did was went back to EJ207...