Sounds like the engine is on it's last leg... so... what I would use is either of these... (for smoking)
Rislone Ring Seal
Restore for the 6 cyl
Either of these can be found at Autozone or your local parts store.
I have used the Restore before and it seemed to help.
Now, on you shuddering at idle or coming to stop sign and it shudders to almost die.. this sounds like the IAC valve not working properly. (Idle Air Control Valve controls the idle speed) http://www.autozone.com/R,1966109/ve...ductDetail.htm
These have a tendancy to get clogged up and not work very well.
Also what might be the culprit is the EGR valve. http://www.autozone.com/R,189875/veh...ductDetail.htm
It may be stuck open a hair with some carbon build up around the valve which will cause a miss/hesitation/rough idle/dieing at stop signs.
These can be removed and cleaned with "some" success just replace the gaskets with new ones.
There are more things that might cause your problem but these would be my first "look at's"
Hope this helps ya some..