Sorry. I meant behind the rod that connects to the stop lever. It is indeed down on the IP. You will need a Deeep socket to loosen the locknut first, then you can turn the idle screw, be sure to try and hold the screw still when re-tightening the locknut as it can turn the screw with it and send it out of adjustment again.

Easy way to do it: Hand tighten locknut with long socket by hand (hold the socket) and keep a flathead screwdriver on the screw to keep it still. Once the locknut is hand-tight you can switch back to using a ratchet to tighten it down and there's no need to hold the screw still anymore.

I took your picture and pointed out exactly where it is:

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