Hi,
The pulse sensor tells the ECU when the second bank (on which #6 is) is lined up for injection. Perhaps the system has a limp mode that batch fires all six when it can't detect the #6 sensor. If this is the case, then idle won't be significantly affected.
Sounds like you have tried all the usual suspects - boots, bellows, ICV hose, intake hose (the one buried under the manifold), booster check valve...
Have you checked the tee fittings on the hoses? If I recall, there is one somewhere. How about the oil filler cap? Dipstick? Crank position sensor?
Hope you solve this.
Regards,
Adnan