Thanks for the reply, no choking/shaking, just the untimely shutdowns. Took it to a competent mechanic, who examined the EGR valve, and says the diagnostics he ran on the valve showed it was OK, so he's going to clean it up a bit. Then he looks at my car (with its 185K on it) and says "have you ever replaced the cables/rotor & caps? It all looks like original equipment, and by the way, it wears out!" So, he'll do a complete tune-up, and then resume...