Worth checking that the back box hasn't grown a tail. Quite common for the stuffing to escape and block the exhaust.
Ah yes, that had escaped me. But a possibility. It doesn't always show as it can collapse internally and block the exhaust (creating high exhaust pressure and thus affecting combustion)
As a guide, here are the things to check (in order of ease):
- exhaust blockage (have a look inside with a torch or put hand over the exhaust outlet. At idle, when the engine is cold you should feel a distinct yet slight and regular pop in the exhaust gas. if you know someone with known good v6 miggy you can compare the 2)
- check multirams are working (both at the front trumpet and the rear of the plenum, many require scuttle to be removed)
- Check plug wells for oil/water
- change fuel filter if not fairly new/unknown age
- Check/replace HT leads (with a decent multimeter you can check the resistance)
- Check/replace plugs (check for pitting/damage/wear)
- check/replace DIS pack
If you are unable to do any of these I am sure there is someone nearby that can help
