...sensor

Ok so it's been a long week.
Chicken or Egg delimma.
22re, '89 4Runner, A/T. I'm am geting an error code for the kock sensor. Didn't even know, just happened to be setting my idle awhile back and noticed it.

So - do you replace the sensor b/c it's throwing a code, or is its job to throw a code b/c something else is wrong causing the "knock"? Does the sensor actually adjust something?

Why was I setting my idle? B/c it's mighty rough. If I set it at the spec-ed 750 RPMs, once nice and warm, it shakes and rattles the whole vehicle. Engine dosn't sound bad, but when I adjust it by "ear" so that it sounds good, and is more comfy at idle, it's more like 850 or so. Note that at 950(ish)+, it sounds/runs just fine.

Suggestions? Could this be a motor mount issue?