i have a 98 frontier 4wd, 2.5L standard, over 300k KMS. i used some seafoam spray intake cleaner the other day to clean my intake because of an idle issue, which was fixed with the spray, it was just dirty. the trouble is now, the truck smokes worse than my 2stroke motorcycle! it does get better after being warmed up, but cold it is embarrasing for anyone behind me. if i keep the revs very low but the throttle open to keep the vacuum down some, and it does make it better. i know it sounds like valve seals, but why all of a sudden would this happen? also, the rattle i had always attributed to the timing chain tensioner has miraculously disappeared as well! i did an oil change after this started, 10w30, and it hasnt made a lick of difference. so. what might the issue be? will valve seals fix the problem? is there any stop smoke product that actually WORKS? how hard is it to do the valve seals on these motors? thanks for any help!