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VinceSA
12-20-2016, 03:27 AM
Hi Guys,

Greetings from sunny South Africa.

My wife and I both have 2007 Yaris 1.3 manuals. My wife's Yaris (Has 117k on the clock) and has picked up an issue which Toyota are not able to sort out. When the car is hot the revs drop to below 400 rpm, the engine starts to shake and the car eventually cuts out. Sometimes the revs are so low that the rev counter does not register at all.

Symptoms:

- In start/stop traffic the car's revs drop (less than 400rpm), engine start to shake and eventually car cuts out
- Twice in the past week, the car idles abnormally high +- 1750rpm (normal operating temperature). This lasts for about 5 min and then goes back to normal.
- Intermittently the car also seems to have an abnormal flat spot below 2000 rpm in second gear/low RPM
- My wife has also complained about the car jerking in heavy start/stop traffic i.e. 1st, 2nd low revs then stop
- Whilst driving the car myself the past few days at an intersection, the car started idling low and shaking, I then tried to get the revs up, pushed the throttle with no response. After a few seconds, the car "woke-up" and I managed to give it a rev before making it across the intersection (thankfully before being T boned by oncoming cars)


A couple of clues:

- Only happens when the car is hot (+- 20 min of start stop driving)
- Intermittened problem - does not happen all the time
- Seems to happen more easily when its hot outside
- Aircon/lights etc make no difference - does it irrespective

So far Toyota have swopped/done the following:

- Cleaned the throttle body and MAF sensor
- Replaced the throttle body
- Run diagnostics - no error codes
- Disconnected the alarm and anti-hijack
- Disconnected battery to reset ECU/fueling/throttle position

I have done the following:

- Swopped the battery with my Yaris
- Swopped the MAF sensor with my Yaris

I am afraid the problem still persists.:help:

Otherwise the car runs perfectly. She is regularly serviced, returns good fuel economy etc. In every other way, its the same as my Yaris.

Do you guys perhaps have any suggestions?

KimmoKekki
12-20-2016, 06:22 AM
Heloda [emoji1360]
Luckily you have 2 exactly samekind of cars !
So if you are petrol head and have some tools then just swap parts from car to another !
Temperature sensors and fuel pump came to my mind first !

VinceSA
12-20-2016, 08:26 AM
Thanks for the reply.

Just two quick questions:

- Where would I find the temp sensor/s? Are there more than one?
- Where would I find the fuel pump on a Yaris? Do they normally give problems?

Silly questions I am sure - not much of a mechie myself but willing to learn.

KimmoKekki
12-20-2016, 09:44 AM
Intake air temp semsor is on intake boot or at air cleaner case ...
I don't actually know where water temp sensor is located on Yaris engine !
And don't know either how many water temp sensors it has !
Stacking fuel pressure regulator can make this kind hassle too ..

Fuel pump is in tank under floor pan and locates under rear seat ...
on hot conditions like in RSA everything is possible !
Changing one part at a time you'll find the malfunctioned one for sure

jra
12-20-2016, 07:41 PM
Like Kmiokekki said, it could be a lot of stuff. If it only does this after engine is warm, it must be temp. related. Maybe ox sensors, front sensor could be getting carbon build up and telling computer exhaust is cooler than it is, causing computer to think rear sensor is to hot compared to front one, so it leans fuel mix? Or EGR valve hanging up, although Toyota has very little trouble with them, could be something to check.

Bluevitz-rs
12-20-2016, 10:03 PM
You'll need to get a bunch of readings from the OBD port with a scanner.

Coolant temp
Intake air temp
Fuel trims (Long term and Short term)
O2 Or AFR sensor readings from B1S1 (Bank 1 Sensor 1)

KimmoKekki
12-20-2016, 10:48 PM
Hey jra .. read my name again mate [emoji102] it's kimmo

VinceSA
12-21-2016, 02:02 AM
Thanks for the advice thusfar.

Re the temp - diagnostic machine said coolant temp within normal range. Fan comes on as usual.

VinceSA
01-06-2017, 02:55 AM
Hey Guys

Some feedback, which I hope helps anyone with similar issues in the future:

Issue turned out to be the two oxygen sensors that needed to be replaced.

Some interesting points re this issue:

- Apparently the relevant oxygen sensors only kick in when coolent temp over 70 deg celcius
- According to the ops manager at Toyota (the guy who eventually solved the issue) - he had the issue on 3 yaris' before. All located in Cape Town (coastal) - my wifes was purchased in Cape Town
- R4800 in total for sensors and labour (1 hour)
- Faulty sensors did not come give error code on diagnostic equipment

I hope this info helps someone in the future. What a mission to pinpoint what it was.
Thanks again for all the assistance/advice!

guybloom
08-01-2019, 11:34 PM
Hi Vince

I like your post, very descriptive and useful. I have a relatively new 1.5 Yaris 2016 model with 70000 km with a new battery. I have an odd idle issue.

When car is hot everything is good. However, after driving for a while then turning off, then restarting for a short drive. Car will idle low to almost cutting off. If I keep reving and driving it will be ok after 20 minutes drive.

Any help on this ?

kharrison5775
12-09-2020, 11:43 AM
I have been to Toyota Table View and after 2 days they cannot locate the fault. No error message being displayed and all diagnostics reset.
VINCE - which Ops Manager in SA helped you?
Thanks