GM-GMC: engine gmc truck, gmc truck, oil conditioner

Question
i have a 1996 3/4 ton gmc with a 5.7 vortex motor.  engine light is on, when put on a obd2 it shows code number po507-mechanic said not an issue.  the truck started using oil and the tail pipe got jet black.  truck was iddling rough-put in some lucas oil conditioner.  oil stayed clean, no smoking, rear seal has a little leak.  have you any ideas for me

Answer
The code that you listed (p0507) is for the idle control circuit.  If you are having idling problems or a rough idle I would say it is an issue.  If the problems have gone away than I would say it isn't an issue.  As for the smoking and burning oil, I would ask how many miles on the engine and how much oil does it burn. Every engine will burn some depending on a wide variety of factors.  
I would say if the smoking is gone and the idle is better, keep doing what your doing?!  If it ain't broke, don't mess with it.  If it is broke, repost and I will help you as best I can.
Hope this helps