02 4wd with 117k miles. Started to get the dreaded grey/blue smoke at cold startup. Lasts for about 10 seconds and then goes away. Only happens at Cold startup in the mornings or whenever in the middle of the day when the car has been sitting for awhile. My research has told me that the most probable cause is bad valve seals. Is it worth doing a compression test first? Any other tests I should do to rule other things out? Also how do I know which valve seals are the problem, or should I replace them all at once. And finally, can someone point me to a post or video on this procedure. I've seen plenty of videos so far but not specifically for the 1AZ-FE 2.0L engines.