new idling problem

My car just starting idling up and down and then settling to an idol at about 600 rpm. It usually stalls out a few seconds after that unless i throttle it up. It then will stick at a higher rpm. And when driving it will shift a little harder than usual and when you let off at about 45 the gearing will slow you down rapidly. I tried a code reader but it said it was not plugged in. Any ideas guys?

and the exhaust is hot as hell after running it for awhile...could it be clogged?