My 95 TSi is having problems with detonation when the car is under load but while still in vacuum. For instance, off the line will be fine, shift into 2nd and it'll detonate once or twice, and then cruising up a hill in 3rd or 4th at part throttle but NOT in boost, it will detonate like crazy. As soon as I give it more throttle and it starts building boost, the detonation goes instantly away and it pulls strong.

Since it's a 1995, the crank and cam angle sensors are both behind the timing belt and non-adjustable as far as I know.

I checked the timing and it's 8*BTDC under normal operation, but drops to 1-2*BTDC (spec is 5* +- 3) when I ground the brown ecu wire. So base timing is barely in spec, retarded slightly.

Only mod is a 3" catback. Have tried brand new:
- Magnecore and Champion plug wires
- NGK and Champion stock plugs gapped to .035
- Bosch and OEM O2 sensors
- PCV valve
- Cleaned oem 450cc injectors

Plugs look (and car smells) like its running a little rich. The plug wires look like they're arcing to the cruise control cable a lot, and theres several burn holes in all 4 of the wires anytime they're near a convenient ground. No CEL's. No other issues.

Please give any suggestions you can think of, I'm pretty much out of ideas.