Here is a video of the EGR tubing conditions. The tubing is clear but there is oily deposits inside and the intake manifold has oily deposits.
Rob have u found the cause yet? We have a Prius w same issue. We have the misfire on cyl 4, moved plug coil pack and injector, compression tested and still cyl 4.
What was the readings of the compression test? If I've got this right: #4 piston is last in line on driver's side? This is the side EGR gasses enter.
Test drove it just now, it feels like the stumbling issue improved. Your issue sounds like a mechanical problem that is unique to that cylinder. Compression testing is in order?
If you moved the plug and coil to a different cylinder and the cylinder remained the same, the issue is with the cylinder?
The wiring harness for cylinder 4 could have issue along with module that sends signal to that coil. So it still could be electrical problem, after I thought about it. A grounded test spark plug might show loss of spark...
Since you live in Orlando, Fl., where there a plenty of E0 stations, I'd try some E0 gas before any mechanical or electrical solutions. Go to pure-gas.org for a bunch of E0 station addresses. Many WAWA stations.