1996 Intrepid Surging

My 1996 Intrepid, 3.5 engine, has been doing what I call surging. When slowing down to come to a stop or slowing down to let it coast it will act like it's dying then pick back up, it does this for a few times then might go ahead and run fine. Also, when taking off slowly it will do the same thing, sometimes almost to the point I think it's going to die. It usually doesn't die, has only died one time while in park and idling. If I take off fast it won't do it but will about throw you into the back seat and when just sitting and idling it will go up and down in rpm's to the point of almost dying then revving up fast and back down. It has had the o2 sensor changed twice and the egr valve changed, due to it showing the o2 sensor on the diagnostics when check engine light came on and the same with the egr valve, due to light coming on and showing that as being bad. It doesn't do it when they put the diagnostic tester on it or when one of them drive it but will with me and when others are with me. The garage tells me they can't fix it if they can't find the problem. I thought someone here might know what it could be that is causing it. I can't afford to keep putting parts on it and it doesn't help it so if anyone might have a suggestion I would greatly appreciate it.

Thank You

I got a 95 vision with 310k on it... does the same thing.... I cleaned my throttle body with cleaner and a toothbrush.... that helped A LOT. got dirty in like 3 months , so again.. I cleaned it... it helped a little bit...... but I found oil in the the cylindrical thingy between the air filter box and the throttle a lot of it... I think that has something to do with it. I dunno man.