Been on the same set of Denso Iridium TT spark plugs for the past 40k-50k miles, about 2-3 years. The car now has around 95k and I am freshening things up. The #1 cylinder spark plug's electrode looks round, like a sphere or tiny ball bearing. The #4 is missing its electrode tip. It explains the extra rumbles when A/C is on and what seemed like a very slight misfire or hesitation that happened very infrequently. Obviously, those went away with the new plugs (NGK Ruthenium HX, also twin tip).

Did a compression test while I was there and especially due to the damaged plugs. Cylinders #1 and #2 had 189. Cylinder #3 is 191. Cylinder #4 is 192. All held their compression fine.

The only culprit I can think of is maybe the intake tumbler flaps are not functioning properly. I've been wanting to run some tests on that system for awhile. I know I can test the vacuum components for this system and the actuators, but I don't know how I can visually inspect the flap conditions.

I can post higher quality pictures of the damage plugs, if requested.


Denso Iridium TT after 40-50k miles/2-3 years