52--Knock sensor

You mentioned that the knock sensor wire runs along the head, but where exactly is it? Left or right bank? Front or back? Any idea of what one of these costs and is Toyota the only source for the part?

The KS wire runs along the left head(Drivers) underneath the intake plenum to where the KS is located between the two heads, The only way to get to it is to remove the intake manifold, this is why Toyota recommends switching both whenever head work is done.

IIRC when I bought my current KS/KSwire(4yrts ago) it was about $145 for the KS, and the KSwire was about $45, unfortunately not cheap and are a dealer only items, or parts store that buys from the dealer(at reduced costs), they usually run about 20% less than the dealer. There are also some Toyota dealers that sell on the web, their prices are usually 25% less, no sales tax or shipping(above a certain $ amount).

You could have the dealer test your KS, if you ask the parts counter guy, it could be free, and just buy the KS wire, that is if you do the work yourself. Removing the intake plenum isn't all that hard, the FSM(Factory Service Manual located at the top of the forum will give you a step by step removal/install instructions.