Last Saturday I spent some time changing the plugs in my stock '02 WRX. Not as bad of a job as I thought it would be, it was actually very straightforward (I noticed the factory used a small amount of threadlocker on the bolts that retain the coil packs to the heads).

Anyway, after finishing the job, I took the car out to San Gregorio out on Highway 1. I immediately noticed that the low-rpm, large throttle opening stumble I was experiencing prior to the plug change was GONE. Now the car simply responds, even when cold.

I am wondering: is this due to the plugs dying (after 24,000 miles??)

OR is it due to the fact that I had to remove the battery to access the LH bank plugs (and in turn, reset the ECU)??

Any ideas? The plugs I removed were definitely worn (center electrodes were rounded off, same with side electrode) , but otherwise were clean.

thank you,

 

It most likley was because of the plugs.