Intermittent Jerking and Idle Stall on 2007 Yaris 1.3 (2SZ-FE) with –20 % STFT - Toyota Yaris Forums

Or05230 · 06-05-2025, 09:19 AM

Hello everyone,

I’ve been battling an intermittent drivability issue on my 2007 Toyota Yaris 1.3 L (2SZ-FE) and could really use your insights. Below is a summary of what’s happening, what I’ve tested so far, and some live-data readings. Any ideas or suggestions are greatly appreciated!

1.Primary Symptoms:

- Jerking under light throttle or cruising – It feels like the ECU is abruptly cutting fuel when the STFT drops into large negative trims.

Occasional idle stalls – Usually when stopping or coming to a slow roll (e.g., at a stoplight), the engine will dip toward 600 RPM and sometimes stall altogether.

Variable occurrence – It does not happen every time; sometimes I drive for 30 minutes without incident, other times it happens multiple times in a single trip.

in any case, once warm, the idle is pretty low w/ the AC off.

2. Key Scan-Tool Data (Warm Idle)
Short-Term Fuel Trim (STFT): Dips as far as –20 % right before the jerking/stall.

Upstream O₂ (Bank 1 Sensor 1): Cycles smoothly between 0.07 V ↔ 0.70 V at idle (≈1 Hz oscillation)—indicating a healthy heated zirconia sensor.

Downstream O₂ (Bank 1 Sensor 2): Steady at 0.60 V – 0.65 V, as expected with a good catalytic converter.

3. What I’ve Already Checked
– Pretty new NGK OEM Plugs.

MAF Sensor & Intake:
– MAF reading at idle = 1.2–1.4 g/s
– Throttle body cleaned (top and bottom).
– Intake manifold and vacuum hoses looks ok.

-Coolant temp looks accurate.

No Stored DTCs:
– ECM logs no check-engine light, no pending codes, no misfire codes, no O₂ or sensor faults. also tested by 2 mechanics with Toyota special OBD.

Thank you!!!

robkay · 06-30-2025, 07:40 PM

Hey, I might be having the same problem. At least similar.

2007 Hatchback. A couple weeks ago I noticed when I was slowing down to stop I had the same sort of symptom, although it did not stall. I switched off the A/C and the problem did not continue, but that might have just been a coincidence.

I mentioned it to my wife and she said she noticed it once the day before but didn't say anything because she thought it might just have been a fluke.

A couple days later she drove it again and said she had a lot of trouble with it. She was worred that it was going to stall out on her, although it did not. She said it didn't matter whether the A/C was on or off.

I took it to a reliable local shop. They had the car for a week and guys drove it and said they didn't have any problem--except the owner commented that when he was driving it in to the lift it made one very slight "bump."

So, we just picked the car up and within a mile of leaving the shop my wife pulled over and said it was acting up on her. So, we switched cars and I drove it the rest of the way home and i didn't have a problem

So, as you say, it's an intermittant issue. It's unsettling because you don't want to get stuck somewhere.

Oh--I checked for stored codes with a BlueDriver and there was nothing. Strange this is happenind and no stored codes.

I hope someone can offer some insight on this for us.

06-05-2025, 09:19 AM	#1
Or05230 I've made a post! Drives: 2007 Yaris Join Date: Jun 2025 Location: Better to keep in secret Posts: 1	Intermittent Jerking and Idle Stall on 2007 Yaris 1.3 (2SZ-FE) with –20 % STFT Hello everyone, I’ve been battling an intermittent drivability issue on my 2007 Toyota Yaris 1.3 L (2SZ-FE) and could really use your insights. Below is a summary of what’s happening, what I’ve tested so far, and some live-data readings. Any ideas or suggestions are greatly appreciated! 1.Primary Symptoms: - Jerking under light throttle or cruising – It feels like the ECU is abruptly cutting fuel when the STFT drops into large negative trims. Occasional idle stalls – Usually when stopping or coming to a slow roll (e.g., at a stoplight), the engine will dip toward 600 RPM and sometimes stall altogether. Variable occurrence – It does not happen every time; sometimes I drive for 30 minutes without incident, other times it happens multiple times in a single trip. in any case, once warm, the idle is pretty low w/ the AC off. 2. Key Scan-Tool Data (Warm Idle) Short-Term Fuel Trim (STFT): Dips as far as –20 % right before the jerking/stall. Upstream O₂ (Bank 1 Sensor 1): Cycles smoothly between 0.07 V ↔ 0.70 V at idle (≈1 Hz oscillation)—indicating a healthy heated zirconia sensor. Downstream O₂ (Bank 1 Sensor 2): Steady at 0.60 V – 0.65 V, as expected with a good catalytic converter. 3. What I’ve Already Checked – Pretty new NGK OEM Plugs. MAF Sensor & Intake: – MAF reading at idle = 1.2–1.4 g/s – Throttle body cleaned (top and bottom). – Intake manifold and vacuum hoses looks ok. -Coolant temp looks accurate. No Stored DTCs: – ECM logs no check-engine light, no pending codes, no misfire codes, no O₂ or sensor faults. also tested by 2 mechanics with Toyota special OBD. Thank you!!!

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06-30-2025, 07:40 PM	#2
robkay Drives: Hatch Join Date: May 2009 Location: NW OH Posts: 93	Hey, I might be having the same problem. At least similar. 2007 Hatchback. A couple weeks ago I noticed when I was slowing down to stop I had the same sort of symptom, although it did not stall. I switched off the A/C and the problem did not continue, but that might have just been a coincidence. I mentioned it to my wife and she said she noticed it once the day before but didn't say anything because she thought it might just have been a fluke. A couple days later she drove it again and said she had a lot of trouble with it. She was worred that it was going to stall out on her, although it did not. She said it didn't matter whether the A/C was on or off. I took it to a reliable local shop. They had the car for a week and guys drove it and said they didn't have any problem--except the owner commented that when he was driving it in to the lift it made one very slight "bump." So, we just picked the car up and within a mile of leaving the shop my wife pulled over and said it was acting up on her. So, we switched cars and I drove it the rest of the way home and i didn't have a problem So, as you say, it's an intermittant issue. It's unsettling because you don't want to get stuck somewhere. Oh--I checked for stored codes with a BlueDriver and there was nothing. Strange this is happenind and no stored codes. I hope someone can offer some insight on this for us.