I did change back to the Bosch plugs today and it is running fine again. Although the difference in colouration between the two types was interesting. The Bosch plugs when I removed them first time were a beautifull tan brown and the Iridiums had a white powdery, dusting on the very ends.

Maybe I should check the dizzy cap and leads. But with only 60,000 easy miles would this be premature for a worn cap and leads?

Nevertheless, I will check into it as the performance and crispness of the engine with the Iridiums is worth the effort for sure.

To be updated...

Cheerz for the help.