Nissan Repair: idle smoke, holes in the head, valve seals

Question
I'm having a problem with my 95 nissan pickup (2.4 liter 4 cyl, 5 speed manual) when im sitting at a stop sign or red light or when it idols for awhile it starts smoking until i take off and when it sits for awhile and i start it up the engine makes a clattering sound for a couple of seconds and think its the valves but it does it even after i change the oil in it and it burns off quite a bit of oil too what could the problem be and how much would it cost it get it fix any information would be greatly appreciated.........thanks

Answer
It sounds like you have oil drain back problems.  This is where the oil return holes in the head are plugged up.  Take the valve cover off and inspect for sludge.  If oil builds up in the head the oil will get sucked down the intake valves.  Also, you might need to replace the valve seals while the valve cover is off.  I would change to Mobil 1 5W30 synthetic and see if this helps after opening up the return holes.