I drove the Prius twice today, and each time when I noticed it was in hybrid stage 3 (engine continuing to run during low speed glides) I stopped and let it idle until it entered stage 4. The first time I was stopped at a set of lights, and though I didn't time it, it seemed to idle for much longer than usual (about 20 seconds) before it finally cut out. I thought it was probably just a one off anomaly, but when I made the return journey home and tried it again, and this time it idled for 17 seconds before cutting out. Normally it only takes 7 to 10 seconds. I wonder if this is a bad omen, like an oxygen sensor or something is just about to go?
I've had this happen before. For me, it seems to correlate with when the weather is cold or damp.... My guess is that it is trying to find the proper operation conditions (A/F ratio?) to get the magic idle speed (960 rpm or something) and if it has a bit of trouble (due to different atmospheric conditions, for instance) it has to try for longer. Just speculation on my part, though.
Yeah today was very warm here, I wonder if that has anything to do with it. Also my Prius is slightly overdue for an oil change, but I checked the oil and all the fluids and everything seems fine. There doesn't seem to be anything wrong with the performance, apart from just this unusually long idle to stage 4. I'll have to try it again tomorrow and report back.
I think it has something to do with humidity at lower temperatures. During the past few days it has happened twice to me too. Very humid or raining and the temperature in the 15° Celsius range. It also happened after a short stop when the ICE might not have cooled down enough to go out of S4 after going into S4 before the stop.
Ok, good to see that I'm not alone. Anyway here's the update. This only happened the two times that I mentioned in the opening post. It was two consecutive times in the one evening, which made me wonder if something was starting to go bad. However since then it hasn't happened again. I drove it three times yesterday, and each time I let it idle to stage4, and it only took about 7 seconds. Then I drove it twice today, and again both times it was well behaved. So happily everything seems totally back to normal.
