Rough idle at stoplight - dash says motor off

IMHO I think that your car could be 'Dieseling' which could be due to a higher than 'normal' compression or a hot spot cylinder deposit.
As a first check you may want to check the oil level to see if it is within the limits and you may not want to wait until 20k service, an oil pressure within spec may be needed to set the Variable Valve Timing ( which could influence the compression ratio )

From personal experience in my previous cars, dieseling and detonation tends to be a problem in the early spring and a side benefit is that at that time of the year for about 2-3 weeks I get the highest MPG readings.

 

Not a normal issue. Make an appointment and get it examined. You are doubtless still covered under warranty.

Try to arrange things so that it might be reproducible... have them prepared to have a tech on hand for a drive with you in the car. Nothing more annoying than hearing that it didn't do that when we drove it.

Roland

 

Not really sure how right i am here, just a little tip. I heard there is a recall on some priuses, concerning the software update for the engine. Maybe this free update could fix an issue. Good luck
P.S.:
To check your recall eligibility, go to Toyota Safety Recall and Car Service Information and enter your VIN

 

are you running regular gas? 87 octane.

 

something is definitely wrong. how bad are your mpg's?

did the ice misfire before the recall?

 

yes, you never know when or why the ice runs, unless you understand all 5 stages of warm up. mpg is a better indicator of overall health. with my '08, i would rive my commute, which is 4 miles of back roads then 2 miles of highway. even on a 80 degree day, after i got off the highway and approached my office a mile away, going 10 mph through an industrial park, my engine would run the whole time.

 

The key to me is the "rough idle".
I let the HSD decide when the engine should run, and when it shouldn't and unless my MPG plummet, I assume it's making the right decision.

But running or NOT running the engine should not really idle rough. Especially if this is at the end of a commute and the vehicle is warmed up.

Assuming you bought this car new, and it now has 18K, and this behavior has recently manifested? I'd just go have it checked out. The OP is still under warranty.

It's tough if the circumstances are so specific that the dealership is saying they can't duplicate.

How often does this happen? Is it intermittent enough that one could simply consider these rough idling incidents simply "Winter" or "Winter Fuel"?

Or is it happen so often that it IS a real problem?

Even though I think it's benefit is very questionable. I do run a bottle of Techron through my fuel system about once every 10,000 miles.

You could try running a bottle and seeing if that helps at all.

 

In my experience going back to 2006 with the Gen II, the ICE continues to run after coming to a stop for a couple of reasons: 1) the traction battery is full, and the electronics are spinning the motor to deplete battery charge, 2) it's cold outside and you are using the climate control to warm the cabin. Under condition 1, you are not using any gas to run the ICE. In condition 2, you are using gas so that the ICE will produce heat to warm the cabin.

 

for the record, dieseling (after ignition is turned off) is only applicable to carburated engines. The only reason I know it, I have a boat that is hard to stop when hot.

I had one or two instances when engine started and stopped for no good reason when sitting (warm engine, no heating, almost full battery, etc). Some kind of software glitch I think. If I were the OP, I would disconnect the battery to clear volatile memory.

 

I don't think the Prius can diesel. The ICE does not just idle freely, it is coupled to MG1 and MG2. If the ICE is running when it is not expected, you'd bet MG1 and MG2 would complain and throw a code.

As stated above, I think it is hardly plausible for a fuel injected car to diesel. Running an engine requires two things: 1)Ignition source, and 2) Fuel. Once a fuel injected engine is turned off, the injectors are shut off, how does it diesel?

I have read reports of the ICE running excessively with no code, due to battery over temp. Have you checked your battery cooling vent for blockage?

 

have you had it checked for codes?

 

Wouldn't any code light up the dash like a Christmas tree?

 

they don't come on with every code.

 

I've had something similar to this happen when my traction battery was going south. As the traction battery got worse, I could duplicate this trouble anytime. Since (recently) replacing the traction battery I have never had this reoccur.
I actually documented this within minutes of it happening:
Its a warm (80°) at 10AM August morning. All of this is with the AC running.
Starting with a "cold" engine I drove ~2 miles to the Interstate, then drive ~12 miles at 70+ mph.
At my exit I slow down with the brake just enough to watch the regen. bar go fully to the left & slow all the way down 70-to-0 & end up stopped at a traffic light. The battery gauge went up to 1-bar-from-top & the engine shut off (as usual). After 2-3 seconds at the light the engine starts up & idles. I don't remember it idling rough but it may have & I never noted it. The engine idles ~15-20 seconds then shuts off. While at the light I got out my phone & fired up Torque. The BT adapter is always connected & when Torque connected I could see a 0.7V difference between the highest & lowest of the 14 battery module pairs. The rest of my drive was eventful.

In "normal" driving the Prius attempts to keep the battery at 60% State-Of-Charge. Using regeneration braking from 70 to full stop would push the SOC to ~65-67%. One of the on-board computers did not like the high battery voltage & decided to start the engine to perform some test. It fires up the ICE & everything looks OK so it shuts down the ICE & continues.

Eventually it starts setting a "pending code" P0A80. The only way to see the code (or that a trouble might exist) is to use a OBDII code reader.
Looking at the dash lights, there would be no indication of a problem.

At the time I already knew the traction battery had a problem. I had been monitoring the 14 batt. voltages & noted one that was not trending the same as the other 13. Torque worked very well for me, to monitor these voltages.