Weird event earlier today...

I was out and about in my 2009 Gen II (129,000miles) doing errands, and came to a red light at the bottom of a hill, so I stopped - the ICE had been running for 10 minutes and so had warmed up, I had the A/C "on" (set to 74F so the fans were blowing, and external temp was around 40F).

As I came down the hill, the ICE was not running, but at the red-light as I stopped, the ICE was "OFF", then about 5 seconds later turned "ON" for 5 seconds, then "OFF" for 5 seconds, then on then off for about 5 seconds each time!!! …until I switched the A/C to "OFF", and then the ICE stayed "OFF".

It's the first time I've noticed the ICE cycling ON/OFF so rapidly! Sometimes it comes on, but most times it goes off and never cycles - anyone have any idea what might be happening?

BTW (according to my ScanGauge-II) when stopped at the light, the SoC was 74% (about as high as I've ever seen it when the car is not being driven, the highest I've ever seen it when the car is moving is 81%). AuxBat was 13.6V, ICE temp was ~180F.

…any clues? …anyone?

Thanks in advance - Wil