92 Cadillac Seville stalls at idle - why?

I have a '92 Cad Seville with a 4.9EFI engine. After driving @ low speeds it stalls when coming to a stop. It starts right back up & then runs fine. Had a complete tune-up, by a trusted mechanic, it even happened to him but he could not identify the problem -no codes-. Happens infrequently but it happens, runs fine inbetween. This car isn’t driven much, sits for a week at a time, I’ve put a gas dryer in it but have only driven it once since then so I don’t know if that’s a fix or not?? Has this happened to anyone else? Any ideas? Thanks