my car recently has been stalling when i come to a stop, it starts to idle below

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1 rpm. i just had a tune up, oil change and otherwise it runs pretty good and smooth. This wasn't happening before. Also just replaced the speed sensor and it has passed inspection. I'm hoping its just a spark plug adjustment. What could cause this I am divorced so when I go to a shop alone they could tell me anything and I wouldnt know the difference. The car has been well maintained. Any suggestions ?