Vehicle shut off intermittently on Weds, was told not fuel pump. Recent tune up.

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Happened Weds, 1st time wouldn't start when I came out of store; got it started after 20mins, then it stopped when idling at red light, kept trying until 45 mins later it started again. Shut off when got home. 3-4hrs later my brother came to pick it up, it started, but stopped again before he could get it to mechanic it stopped again. Pushed it to mechanic; mechanic says not fuel pump and problem has not happened again in the 2 days he's had it. Tune up a month ago.