Heat soaked engine hesitating around 1,800-3,000 RPMs, jerky motion when it picks up power?

Tiny
NANDOR
  • MEMBER
  • 2008 OPEL CORSA
  • 1.2L
  • 3 CYL
  • 2WD
  • MANUAL
  • 111,000 MILES
Hi, I was driving around 300 miles in 93*f heat and the engine developed this hesitation/sluggishness around 1800-3000rpm. Got a check engine light for o2 sensor, no fault code in particular, which I have suspected since the pre cat o2 sensor had to be changed 2 years ago. The next day I have installed a used pre cat O2 sensor and cleared the code and it fixed the issue I thought.
After further investigation, O2 pre cat and post cat sensor was reading correct voltages, I then wanted to check the MAF sensor since it is a common suspect, but my car only has an intake temperature sensor and a map sensor. Cleaned the Intake sensor, and was reading correct air temp. I have then checked my values during load with an OBD2, and the thing that stood out was the air fuel ratio, climbing from a steady 14.6 into the 29's, Map sensor also reading questionable readings. Suspecting different things firstly a bad MAP sensor/o2 sensor/ catalytic converter/ air inlet temp sensor.
Wednesday, July 30th, 2025 AT 10:23 AM

6 Replies

Tiny
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  • 5 POSTS
O2 sensors and trim values.
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Wednesday, July 30th, 2025 AT 10:25 AM
Tiny
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Questionably lean air/fuel ratio
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Wednesday, July 30th, 2025 AT 10:26 AM
Tiny
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RPM/Map sensor/Throttle position
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Wednesday, July 30th, 2025 AT 10:29 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
The post catalytic converter oxygen sensor does nothing for how the engine runs; they just monitor the cats performance. Does the exhaust system have a leak? This will cause the oxygen sensor codes and these readings, btw what is the code number? The fact that you cleaned a sensor and fixed a part of it is telling me it can be a bad MAP sensor with these readings as well.
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+1
Wednesday, July 30th, 2025 AT 10:53 AM
Tiny
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I am aware of the O2S2 checking catalytic performance, I will have to check for exhaust leaks. Currently no error codes, (don't know the original error codes since someone plugged in his OBD2 and as I've glimpsed on the O2 sensor malfunction I knew I just had to replace it since these O2 sensors keep going bad approximately every 2 years and I just went and replaced it the next day) but still there is a remnant of the main issue I had that are showing up in these diagrams. Engine runs much better, pulls through all RPM but still I can feel that something is wrong related to what numbers the ECU uses to calculate the air fuel ratio. I should check for exhaust leaks, vacuum leaks and a clean of the MAP sensor next I believe.
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Wednesday, July 30th, 2025 AT 11:53 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
Yes, good call, here is a video to show the best way to check for vacuum leaks:

https://www.youtube.com/watch?v=LRKWV4Are5c&t

If there are no leaks, I would replace the MAP sensor. Let us know how it goes.
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Wednesday, July 30th, 2025 AT 4:53 PM

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