Have any of you ever seen something like this happen before?
The MAP values universally increased by ~10kPa+, it did not become erratic. The motor started running rich all the way home. Prior to this point the AFR was in the mid 14's as you can see from the attached .jpg. The car started up again on the key twist once I got it home and it idled at the proscribed 8-900rpm. Didn't measure what the MAP value was but the WB AFR was reading 13.5 or so. Maybe its just something that re-sets itself.
Very odd. I think I have encountered this once before. I was driving around for a tuning scan, and the BLM's were looking pretty good. And then they just dropped without any change to the rpms or driving surface or anything. I was running along the sidestreets in our development.
I've attached a .jpg of the scan at the moment this happened. You can see that the MAP value (shown as User 1) here just increases while the AFR at the top starts to drop right after that. And the MAP value stays fairly constant after the increase.
The numbers to the right of the graphs represent the value at the scan position for the perpendicular line.

 

Maybe a small vacuum leak somewhere?? I wonder if that would cause the computer to add more fuel since the TPS remained the same... A vacuum leak would at least explain the increase in kPa.

 

EGR or Canister purge could be the culprit. If EGR is being commanded and you don't have it blocked off it can open up to atmosphere creating the vacuum leak. See if the coolant temp changes right when the vacuum leak pops it's head.
I have a feeling it's one of those 2 things but it's hard to tell without searching.

 

Thirdgen/Jon,

Thanks for the responses. Thirdgen, the ECM would add more fuel simply because the MAP value has increased moving it to a different cell in the VE table. The ECM "thinks" the motor is under more load. The EGR is physically blocked and also disabled at 1B3 in the bin. The 7747 has the canister purge "ON" all the time. I've shown this to some others, and the fact that the increase in kPa is uniform, not erratic, would TEND to rule out a valve or spring problem. If it was a vacuum leak of some sort, its pretty well regulated. You would think the kPa would swing randomly. The vehicle starts and idles fine. I am going to start by checking the MAP sensor first and look at the plugs. I'll also go back to a previous bin.