My 06 WRX wagon with 43K doesn't see many miles and most of my maintenance is done on the 'time' side of the schedule.
It came from the factory with Iridium plugs.
Recently, it has begun intermittently making a 'chk' sound and I can feel the car jerk very slightly. No CEL. I waited till the tank was nearly empty, put in some SeaFoam and filled it up. No help, No CEL. It may be on its 3rd or 4th tank so, I doubt it's a fuel issue. I did pull the MAF connector to force a CEL so I could get FreezeFrame data with my scanner. Fuel trims were all low single digits (dunno what else I should look for there)
This weekend, I swapped out the plugs. And of course, all four I removed 'look' pretty good. Sigh - well, I have new plugs in even though the old ones probably had another 20K or more life in them.
Car still has the miss. It is very random. never seems to do 2 in quick succession, and there could be one, followed by another in 300 yards, or it might be a mile. I have an 11 mile commute on side streets. I have heard it at idle maybe 2 times. I THINK I've heard it decelerating 3-4 times. Of course, at high RPM I can't really hear anything so, not sure if it's happening. But cruising around at 1800 to 3 K or so, it could happen 10-20 times on the way home.
so, I figure I may as well ask what you guys what you think. If I were gonna change something, what would it be (crank angle sensor ?) or even take it to a dealer (what would they be able to do?) I'd really rather not just wait until a CEL comes on or something breaks.