How to save fuel while idling?

I got this international truck and when I idle it for a minute or two it will shut off itself, before shutting itself off, there'll be a "Engine Warning" light come flashing on, after a few moments it will shut off, now if I put on the cruise I can idle all the time, the only time it shuts off whiling idling is when I'm not using the cruise mode, and I got an idea of saving fuel:

I figure when you use cruise mode, it uses fuel, so what I do is I cruise for 10 seconds then I turn off the cruise for about a minute or 2, then I turn the cruise on again for another 10 seconds or so, and turn it off again, and the cycle repeats, does that save fuel, I mean I can only do that while I'm waiting at the shipper/consignee, of course it's not practical if I go to sleep, but if I'm waiting at the shipper/consignee, then I'll do this method, I mean the truck still keeps cool, and I can save some unneeded cruising, is this method practical?