erratic AFR's (but not always) long after warm-up - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-27-2014, 11:02 PM   #1
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Default erratic AFR's (but not always) long after warm-up

I am getting odd fluctuations in AFR and corresponding bucking or surging from the engine long after warm-up. It does not always happen. It may happen at highway speeds or stop and go traffic. It has even happened while in grid at autox's. Obviously when it happens at idle it makes the idle oscillate and more likely than not will stall the engine.

It only does it as mentioned before, well after the engine is running. The log I have is from 2800 seconds of run time and on but it will do it a few more minutes before that. When in traffic and the fluctuations kill the engine, it will stay fluctuating after start-up so it doesn't go away after a key cycle.

I initially thought it was noise causing AE through false TPS signal but that doesn't seem to be the case. What I do notice is a corresponding fluctuation in MAP, some in RPM. But that would make sense since the engine is surging.

WTF could this be? Could it be mechanical? Bad map sensor? VVT doing something its not supposed to? Just really bad tuning? Maybe heat affecting a component in the ecu? If that's the case it would be weird as halfway through the log the issue went away and I didn't stop so heat shoulda been the same inside the ecu. Thoughts?

Had to zip the log as the size (3.8M) was apparently too big.
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erratic AFR's (but not always) long after warm-up-afrlog.jpg  
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Old 05-03-2014, 10:29 AM   #2
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No one has encountered this before? Any and all suggestions are welcome!
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