After spending awhile searching for the final batch of quests that would get me to 160 for Vashj, it appears that there aren't that many quests available just yet in this zone (unless there are quests available after the Throne of the Tides instance). If you've completed the 20,000 leagues under the sea achievement, you've basically finished it for now.
Here is some discussion on the topic...http://www.wowhead.com/achievement=4869/sinking-into-vashjir#comments (http://www.wowhead.com/achievement=4869/sinking-into-vashjir#comments)
i think there is i dont know yet but only halfway unto the zone and at 130
This now appears to be fixed. Logged in earlier this evening and I had the achievement. Somehow, I gained 15 quests while I was offline ;)
My understanding of it, is that there was about 15 quests that weren't being counted towards the achievement.
I thought for sure i was gonna find 160 but only found 152
I saw shadow get it last night, so it is possible.
Edit: Got it at 140 Quests.
howd you get at 140 ive done 152 there and dont have it
I dunno, i thought i was massivly short, then it just went ding,
It may say 140 but you didnt get it at 140. Theres a bug with quest achievements where when you get it, it rolls the count back on the display.