Almost everyone has been in your situation where the dealer says they can't find a problem but you know there is a problem. When a dealer says they can't diagnose a problem, I go to a different dealer. If they diagnose and successfully fix the problem, I write the first dealer a 1 star yelp review, complain, and never use them again. There is also a possibility that your car qualifies for the Lemon Law after the dealer can't diagnose or fix a problem within a certain amount of visits.
My wife had a similar problem with her Odyssey at around 120k miles and I think it turned out being a bad cylinder head, so it was running on 5 cylinders. The CEL was flashing and the engine was idling harshly, but never stalled. It wasn't intermittent like your problem is and was easily diagnosable at our local repair shop. We replaced the idle control valve after it stalled on her twice. This was at 175k miles.
I'm in the process of this now with our 2005 Prius that we are trying to sell. We can't sell it until this annoying A/C problem is fixed. I've had the A/C repaired 4 times in the past 2 years. The compressor was $600 x2. They replaced it and it wasn't fixed. Then the condenser broke once and it broke again a day later. $3k total cost even though all of these parts have a warranty. And it's still broken. They suggest a new part is the problem every time I bring it in. I'm not paying a dime more or I'm reporting them to the BBB. This is despite the fact that my family bought two cars from them. I knew I should have stuck to the independent local shop.