Looks like you've covered everything that I can think of.
I just re-read your original post and noticed this line:
Should I power off the battery and unplug ECU connectors and check/clean?
I only recently discovered that the ECUs on the D3 are just lying exposed in the plenum chamber, and now wondering if that area might be the cause, as I'm thinking that since the symptoms are random in nature, maybe water has got into the ECUs, or at least into the connectors.
Since you replaced most of the vacuum lines, and they're probably worse to get at than on a 3.7 D2, I'd opt to investigate the ECU connector first, and at least rule them out before checking the vacuum lines.
__________________
2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts
Sold!  2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
|