Rpm fluctuates in 2005 jeep grand Cherokee limited

I have a 2005 jeep grand Cherokee v-8 with 63,000 miles on it. When the car is in park or at stop lights/ signs the rpms start To go up and down for no apparent reason. When slowing down it does the same thing with the rpm fluctuation. When I take my foot off the gas the rpms dip way down suddenly and then even out as the car comes to a stop. The check light is not on but I have taken it to the garage so many times it’s comical as they never can find anything wrong with it. I have gotten new spark plugs and a new battery but to no avail.

Any suggestions?

That sounds a lot like a vacuum leak. Do you know what your garage has done to try to sort it out? What kind of a mechanic is it? Many places that claim to do car “service” are not really staffed by actual mechanics.

Another thing that should be checked and cleaned in the idle air control valve (IAC).