Stubborn engine idle problems when hot

[HotRodPrevia]

Hey fellow Previa owners.
I purchased a used previa in 2002 it has served our famly very well with all trac, it's a great snow machine....and when the odometer hit about 230k, the head gasket went, this was ok, because we had already pulled a motor from the junkyard for a rebuild. The rebuild would be attempt to try to make small changes....9.5:1 compression pistons, ported head, gasket matching all throughout, and N/A Toyota cams and dual inlet air box.

Almost a year later we are still diagnosing a engine stumble at idle in gear or when putting in gear when hot. The engine occasionally dies. Our A/F gauge also shows a dramatic jump in fuel vs. air, when the stumble occurs. The engine runs great the rest of the time. We have looked at, cleaned, electrical tested- cleaned and replaced all suspect ground connections, load tested the electrical system, inspected and/or replaced all vacuum lines, tested fuel pressure....a partial list of other areas we looked at include IAC, temp sensors, plugs, wires, rotor cap, coil, ICM - ignitor, vacuum lines etc. Even our local Toyota dealer had it for several days and could not figure it out!

When working on the van this past weekend, I smelled fuel. I did a quick interweb search and came up with injector seals as a possible cause.

Looking for ideas from the more experienced mechanics on this forum, are we barking up the right tree, something else we should look at?