Kapt, your thread is excellent.
Your link to the hack mechanics thread is one that set me on this trail: this sounds like my car:
"Played with this a bit more. Now have the AFM reading about 13.5 at WOT for a variety of conditions.
But now that I have it dialed in better at WOT, I can watch it at partial throttle conditions, and what I'm seeing is that, at steady throttle (say, 65 on the highway), it's reading between 13 and 14, but the moment I crack the throttle, even a little, like to keep up with traffic, it still swings lean, like 15 to 16, whereas if I punch it (WOT), it goes to about 13.5. Then it does a similar thing on backing off the throttle -- it swings rich, like 10.5 to 11, until you lift all the way off the throttle, where it swings very lean, like 16, which has been explained as the cylinders continuing to suck in air.
This is unchanged whether I have the small vacuum hose on the throttle body hooked up to the breather hose from the valve cover, or whether I have the small vacuum hose plugged.
In a prior post, Jimk in Denver wrote:
"With the use of an A/F gauge, a vacuum leak will appear under idle or low load conditons. If the A/F is ok on WOT and also low loads, the problem is not fuel. If ok on WOT but not ok under low load, continue looking for leaks. If not ok on WOT but ok under light load, fuel adjustments are needed. An A/F gauge will also show lean condition if there is misfiring due to electrical causes (i.e., O2 in the exhaust)."
Am I correct in assuming that, even though I have it dialed in better at WOT, this still smells like a vacuum leak?"
And this is what got me thinking I could do better: (curse you bill williams)
"I took the yellow car out and tried to keep one bad eye on the road and one bad eye on the AFR gauge.
At start up and at idle during warm-up, the meter read about 13.2 after a run, the idle reading dropped to about 13.0
I ran the car, on the throttle, cruising and off the throttle. While on the throttle and cruising, the gauge read, with some small variation, around 13.2 to 13.8. Off throttle and it would pop between 14s and low 15s
I had the car around 140 kph (87 - 90 mph) and it still was averaging around 13.2 while getting to that speed and cruising briefly at that speed.
And to be expected, there were the occasional blips of higher and lower reading but just blips"