94 chevy idles to high

I have a 94 chevy blazer 5.7L t.b.i. engine that has been having issues with the idle being to high.I changed out the iac and now you start it,idles at 1000 (to high)then gradualy goes up to about 1800 and stays there.I've checked vacum leaks,checked play in throttle shaft,has a little.I'm not sure on how to check the throttle position sensor or other sensors. checked for ohms on throttle sensor,had nothing while moving it,but drove rig into my garage.I've rebuilt the throttle body with new injectors about 3 months ago,and checked for fuel leaks.all o.k.the e.g.r. valve has been pluged off for awhile but dont know if it would cause a problem after time.It has in the last year a new cat, dist.,coil,02 snsor,muffler tune up,temp sender checked grounds o.k.