Toyota Vitz 2007 Engine Stalling at low RPM

[RusT]

Hi Everyone,

I'm having a Toyota Vitz 2007 SCP90 (2SZ-FE), as of recent when the tank on the car is full, the engine stalls at low RPM (at traffic lights, stop-go etc). But after stalling the car starts again without any issue. This happens often until some amount of petrol has been used from the full tank. Also the car does not accelerate as usual when this problem is occuring.

I recently did a tune up where all 4 plugs were replaced with new Iridium plugs along with 2 injector coils but this did not fix the problem as well.

The second time this issue occured, the petrol pump was replaced as the OBD scan codes showed that the issue was with the fuel, but the issue occured again. I went to Toy#ta L#nka to get a diagnosis and they concluded that the Airflow Sensor/Oxygen sensor 1 was failing.

Kindly note that there are no check engine lights while running, only time check engine light comes on is when the car stalls with a full tank during low RPM, that also goes away when the car is turned on again. The OBD code reading now shows up as rough idle.

I read an old AL thread which mentioned that replacing the MAF sensor fixed the issue for one of the members, but I'm not sure if it will help in my case as Toy#ta L#nka mentioned that the MAF sensor was good, only that the Oxygen sensor needed replacing.

I would like to get your opinion on this issue, as different sources point to many possible causes including EGR valve issues, MAF sensor failing, Oxygen sensor failing etc.

Since replacing the Oxygen sensor costs a significant amount of money, I would like to get a second opinion on what else needs to be checked to diagnose the problem before replacing the sensor.

Any place around the Malabe / Colombo area that would be able to diagnose the issue will also be highly appreciated.

Cheers!

[iRage]

So the car stalls ONLY when the fuel tank is full ? When it is not completely full nothing is wrong with it ?
How do you fill the tank up? Do you stop when the pump handle goes tuck and stops ? Do you keep filling after that until the fuel fills up right to the top of the pipe ? 

<fix is simple ! just don't fill the fuel tank  --- sorry..had to..couldn't stop myself>

[RusT]

Haha 😂 @iRagethat's what I've been doing recently. 

I stop fueling once the handle tucks. 

The current problem is that there's reduced power even when I'm running half tank. But this issue only occured after the stalling problem started. Any leads where should I starting looking to diagnose

Thanks 

[iRage]

Well....the reason I asked how you fill the tank is it could be that the EVAC system in your car is messed up (usually happens when the tank is over filled and the fuel seep in to the evac lines. Over time this can spoil the charcoal canister). The result is that the pressure in your fuel tank will get messed up (this is why sometimes when you open the fuel cap in some cars there is a LOUD LONG hiss sound). When the fuel tank pressure is messed up this can lead to fuel flow issues. Fuel flow issues results in inconsistent power. When the EVAC system goes wrong there are no sensors to actually say that it has gone wrong. But there are some tell-tale signs as well...the hissing sound I mentioned (usually this happens during hot weather or changes in ambient temp too), slight fuel smell when the car is running or soon after running, etc...The charcoal canister in my old Corolla has gone bad. Ever since that has happened I get like 6kmpl where before it would get 10kmpl..so strange things happen.

In addition to the above....I would say start with checking things like the fuel flow pressure, things with fuel filters, etc... 

Another reason is of course the air flow in to the car...I am assuming that since that was already addressed it is more or less functioning as expected. Now here is the thing....if a bad fuel pump or fuel pressure issues exist this could cause a lean running condition (engine not getting enough fuel). This in some instances can cause the O2 sensor to throw an error code. Of course depending on the situation the opposite can happen too...rich fuel mixutre, unburnt fuel, etc....contaminants getting on the sensor...

[RusT]

  On 10/24/2023 at 11:50 PM, iRage said:

Well....the reason I asked how you fill the tank is it could be that the EVAC system in your car is messed up (usually happens when the tank is over filled and the fuel seep in to the evac lines. Over time this can spoil the charcoal canister). The result is that the pressure in your fuel tank will get messed up (this is why sometimes when you open the fuel cap in some cars there is a LOUD LONG hiss sound). When the fuel tank pressure is messed up this can lead to fuel flow issues. Fuel flow issues results in inconsistent power. When the EVAC system goes wrong there are no sensors to actually say that it has gone wrong. But there are some tell-tale signs as well...the hissing sound I mentioned (usually this happens during hot weather or changes in ambient temp too), slight fuel smell w

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Thank you for your insights, and yes I noticed the long hissing sound when the stalling occurred. Opening the fuel cap gives a considerable hissing/vacuum sound. 

I will get the EVAC system and the charcoal canister checked as well.
I'm still getting good mileage therefore would you advise on replacing the Airflow sensor as Toy#ta L#nka suggested. (I plan to use the car for some time).

 

[iRage]

  On 10/25/2023 at 10:38 AM, RusT said:

I will get the EVAC system and the charcoal canister checked as well.

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The charcoal canister is just one point of failure for the EVAC...there are many other things that can go wrong with it. Also...I assure you that 99% of the mechanics will never be able to diagnose an EVAC system failure.