Hello everyone,
I have a similar problem with a Fiat 500 2011, 0.9 Twinair engine. But instead of stalling, this on idles really high, going from over 1500rpms to 1800rpm every 2 sec or so. It has a wideband sensor Pre-cat, and a normal O2 sensor after-cat.
No fault codes stored.
The reason I believe it's doing so, it's because at full operating temperature 93C, the Wideband sensor switches from Open loop to Closed accordingly, creating the up and down idle. in the meantime, as you can see from the picture, the after-cat o2 sensor indicates a very lean condition, while the lambda number for the wideband integrator shows a rich condition!
Now about my findings so far: I discovered that if I disconnect one of the sensors or solenoids, turbo overboost, MAP or Evap or any other, the idle stabilizes to normal, O2 sensor goes to around 0.650 or higher, while the Pre-cat sensor goes to permanent Closed loop. I would have thought it should go in permanent open because the ecu is missing information from the unplugged sensor, but it's the other way around. No changes for the after-cat, stays in Open , but I have tested it by driving the mixture rich, and sure enough it responds going over 0.9V. Don't know why it might not go into Closed. Tested the heaters for both sensors, both are below 10ohms.
The engine revs fine, car drives fine, no smoke, only idling problem.
Another thing would be that the Throttle position changes with the idle fluctuation as well. When idling high, it goes up to 1.0 % then cuts, drops a bit and so on. With sensor disconnected and idling back to normal, throttle position goes down to 0.0 0.1 0.2 0.3 max.
Thing is, I'm not very keen to point towards the throttle body, because it might do this either because it's faulty, or because it is being commanded to do so, because of the switching Wideband sensor from open to closed.
Any ideas, what other checks , please let me know. Next step would be to check the cat for cracks that would explain the lean condition before the O2 sensor, or replacing the wideband for reporting a possible false rich condition. I will let you know about my findings. Thank you!
I have a similar problem with a Fiat 500 2011, 0.9 Twinair engine. But instead of stalling, this on idles really high, going from over 1500rpms to 1800rpm every 2 sec or so. It has a wideband sensor Pre-cat, and a normal O2 sensor after-cat.
No fault codes stored.
The reason I believe it's doing so, it's because at full operating temperature 93C, the Wideband sensor switches from Open loop to Closed accordingly, creating the up and down idle. in the meantime, as you can see from the picture, the after-cat o2 sensor indicates a very lean condition, while the lambda number for the wideband integrator shows a rich condition!
Now about my findings so far: I discovered that if I disconnect one of the sensors or solenoids, turbo overboost, MAP or Evap or any other, the idle stabilizes to normal, O2 sensor goes to around 0.650 or higher, while the Pre-cat sensor goes to permanent Closed loop. I would have thought it should go in permanent open because the ecu is missing information from the unplugged sensor, but it's the other way around. No changes for the after-cat, stays in Open , but I have tested it by driving the mixture rich, and sure enough it responds going over 0.9V. Don't know why it might not go into Closed. Tested the heaters for both sensors, both are below 10ohms.
The engine revs fine, car drives fine, no smoke, only idling problem.
Another thing would be that the Throttle position changes with the idle fluctuation as well. When idling high, it goes up to 1.0 % then cuts, drops a bit and so on. With sensor disconnected and idling back to normal, throttle position goes down to 0.0 0.1 0.2 0.3 max.
Thing is, I'm not very keen to point towards the throttle body, because it might do this either because it's faulty, or because it is being commanded to do so, because of the switching Wideband sensor from open to closed.
Any ideas, what other checks , please let me know. Next step would be to check the cat for cracks that would explain the lean condition before the O2 sensor, or replacing the wideband for reporting a possible false rich condition. I will let you know about my findings. Thank you!
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