I replaced the OE DC0s with "Bosch Platinums" (single electrode) at 15K miles. By 30K miles the idle roughness and emissions problems started. I believe intermittent misfires were causing both.

I switched to Bosch HD9C, and have been using them ever since. I inspect then at 15K and replace at 30K. The idle is not perfect and emissions are still high, but all is better than with the Bosch Platinums.

Nothwithstanding anecdotal evidence, based on my knowledge of ignition and combustion in spark ignition engines, I will not use multiple ground electrode spark plugs.

The archives are full of problems from other than the OE type non-resistor spark plugs. In most cases, installing the correct standard or HD electrode non-resistor plugs solved the problem, but some say that they still had trouble with the HD electrode type plug that went away when replaced with the standard electrode version.

Duke