Hi Grant. Did you ever get this resolved? I have a 2012 with same problem. I am a bit to try a much easier and cheaper fix. There are quite a few posts on forums suggesting ( as per a Lexus bulletin) that the problem could also be as simple as the idler belt tensioner pulley. Can I also ask if you found someone good with ISF in Melbourne? Im in Geelong and need headers done as well.
Thankyou, Carlos.