idling

[mcmurpty110661]

Im quite confused , my engine soemtimes switches off when stuck in travel and other times does not and the A comes on with a cross indicating its not on but i dont touch anything , seems its got a mind of its own

[ColinB]

Plenty of other comments in this forum about the idle-stop (aka stop-start) system, try doing a search. But basically the system is very "picky" about when it will work and when it won't, there's a long list of factors in the handbook that'll inhibit it. The computer is protecting the battery by ensuring everything's exactly right before it'll stop the engine. Some of the parameters are quite esoteric (eg battery internal temperature). The system on my car works fine over the summer months, but hardly at all in the winter. That may be a temperature effect or possibly because journeys tend to be shorter and slower so the battery isn't fully recharging (although the car always starts OK).
One trick that can sometimes reset the system is to remove the negative connection on the battery for a few minutes, then replace it.

[embee]

.... seems its got a mind of its own

Essentially that's hit the nail on the head.

As Colin says, there are lots of parameters the system takes into account before it will "allow" the stop/start to actually function. It's very diffcult to predict whether it will or won't. There are some things which will definitely prevent it working, A/C I think.
Personally I press the off button as a matter of course, but then I don't do heavy traffic so any stop/start benefit would be miniscule for me. It will work reliably if I take the car on a long run, but I don't do that very often these days (£2/litre approaching!!).
I have a 10yr old Yaris with an oldish "regular" lead/acid battery, nothing clever, and the stop/start will operate every time if I let it (again I switch it off as routine), Honda were extremely cautious with the programming of the Jazz mk.3 system.

Live with its foibles or switch it off.

[TnTkr]

If you read the list of functions enabling or preventing auto idle stop system and think each of them through, including the side notes, and you'll begin to understand the behaviour. And also learn how to utilize it other than manufacturer intended