so i have a 1991 w250 12 valve and when i start up the truck it runs fine no blue smoke but when ive driven about half a mile and i come to a stop, a lot of blue smoke comes out. and i mean alot. when i get on the throttle no black smoke just all blue. no loss of power, great idle. im confused on what is causing this and how to fix it?

 

I'd check your exhaust downpipe for oily residue, turbo seals may be leaking. Oil collects in downpipe, then once egt's get high enough after turbo (driving) it starts burning off. To fix, remove turbo and either rebuild it or replace it.