Spark plugs H9DC vs HR9DC (pictures attached)
 

1990 190E 2.6

I was able to get 4 H9DC and the other 2 were HR9DC. I installed them several thousand miles ago and when I took them out to inspect/clean them (I changed my valve stems a year or so back and now its a habit for me to inspect my plugs...clean and dry as a bone!) I noticed the gapping portion of the plugs were different on the HR9DC so I swapped those 2 out for 2 H9DC that I got shortly after the change. Irradic/high/rough idling caused me to inspect my plugs yesterday to make sure there was not excessive carbon build up and they were actually pretty clean. I recently had car smogged on 5/28/13 and at STAR certified station per DMV and passed with all numbers below the average, I think the max for NOx is around 780, I passed that with a 750. Cat was installed same day as smog test. Is there any relationship to the gap of the plugs vs them being resistor type vs the NOx being high (but still passing) vs my rough/irradic idling? Trying to figure it all out to see where I should start searching under the hood. Pictures are attached. The HR9DC plug has a curved end and the H9DC has more of a sharper 90 degree angle end ---> this: ) vs ---> this: ]

I would put it back to see if it will smooth it out, then check for an inadvertent vacuum leak