Yaris Stuttering/hesitating & Engine Light On!

[Toby Unna]

Hi all, new Yaris owner - it's a 1.0 on a W-plate.

The engine light came on soon after buying. Plugged the laptop into the OBD port and it says code p0172, mixture too rich. Car runs fine when cold, but after a few minutes' running and from then onwards it stutters/hesitates badly if you push the throttle hard/quickly, then picks up after a second and goes ok, though it does feel quite flat (even for a 1-litre!)

Cleared fault codes and turned the engine light off, and it's stayed off for 100 or so miles, but the car is still running poorly.

I removed the AFM and cleaned the hot wire, to no avail.

I've searched around and read that stuttering is a common Yaris issue, but wondered if anyone has any pointers before I start replacing bits hat could make the mixture rich - AFM, coolant/air temp senders, O2 senders?

Maybe worth mentioning that the average MPG readout on the trip computer seems pretty good - ~50mph at a 60mph cruise

Thanks!

[Madasafish]

probably a lambda sensor failure.

Attcahed 4 page CM write up on possible failures..

[Raeman]

Hi all, new Yaris owner - it's a 1.0 on a W-plate.

The engine light came on soon after buying. Plugged the laptop into the OBD port and it says code p0172, mixture too rich. Car runs fine when cold, but after a few minutes' running and from then onwards it stutters/hesitates badly if you push the throttle hard/quickly, then picks up after a second and goes ok, though it does feel quite flat (even for a 1-litre!)

Cleared fault codes and turned the engine light off, and it's stayed off for 100 or so miles, but the car is still running poorly.

I removed the AFM and cleaned the hot wire, to no avail.

I've searched around and read that stuttering is a common Yaris issue, but wondered if anyone has any pointers before I start replacing bits hat could make the mixture rich - AFM, coolant/air temp senders, O2 senders?

Maybe worth mentioning that the average MPG readout on the trip computer seems pretty good - ~50mph at a 60mph cruise

Thanks!

Well i've had my sr for nearly 4 years now and it's never stuttered or hesitated yet. Not sure where you've searched that one from but it's not a common Yaris issue.

I would be checking the 02 sensor aswell, this happened once in my Honda Accord, similar symptoms as your Yaris and a simple fix.

[siray123]

I've had p0172 on a different car, it was actually related to a 'Map' sensor, it was basically wiring.

The other thing it could be is the fuel pressure but likely a lambda sensor however i would have thought it would throw a different code.

When the lambda fails it fails lean, thus ECU dumps more fuel in - hence **** idling and increase fuel consumption and flat feeling.

How does it idle, is it somewhat lumpy?

[PhilGee]

Sounds just like the air mass meter fault. When you cleaned it what condition were the pick up sensors like when you looked down the tubed part. From what i gather the silicone covering them goes all mushy and causes incorrect readings. Also, are the spark plugs ok?