My 2004 duramax LLY is idling rough at stop lights. It does that when it's on drive, fully warmed up, and blows out a lot of white smoke with a strong exhaust smell. There is NO check engine light on. When idling from cold start, it's fine. Also smoke goes away when: placed on neutral or park and idle smooths out. Smoke also goes away when driving.

 

Check the idle setting??

 

sounds like injector. get the injector rates checked.

 

yep what he said, really sounds like leaking injector(s)

 

Just changed fuel filter, acceleration improved, but still shakes at idle with fully warmed up blowing out a lot of white smoke, only when in gear (drive or reverse). When it was 50 degrees the other day, it did not shake and smoke. It seems to occur when cold outside (ie below 50 F).

 

Could be a torque converter?

 

does it only do it while the engine is cold? if so then it sounds like the glow plug relay a duramax actually cycles the glow plugs on and off while the eingine is running until it warms up so that would be possible....if it does it all the time then it still sounds like leaking injectors so you still need to have the balance rates checked on them....at idle is the only time that the engine is in the balance mode, as soon as you touch the throttle the balancing shuts off