I did all that too, but my voy still runs like crap. It feels like its misfireing but doesn't thow codes. Feels bogged down.Just finished changing the spark plugs at 96,000 miles. Won't say how long it took. Suffice to say that when I started the sun was shining. When I finished it was still shining (same day).
I had no problems with the old plugs. The Envoy was running great. When I finished, it ran like crap and threw code PO300 "multiple misfires". I tried everything. Even took out all plugs to check for cracks. Reinstalled coil packs. Pulled the battery cable to reset stuff. No good.
Then I cleaned the throttle body. All good after that. I suggest cleaning the Throttle body be part of any plug change.:m2:
Thanks for the the write ups. I must have read them all.:crazy: