EML Lights - 1999 Yaris 1.0

d215yq

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Hi all,

The family's 1.0VVTi Yaris is due for MOT, but has the EML on (been on happily for 2 years apparently but is only now a failure).

So I disconnected the battery for a few hours and refitted it and the EML has gone out and stayed out for 10 miles but the car seems to misfire on full throttle and idle a bit worse than before. It seemed to get better as we drove though.

Is it normal on this age of car that it would have to "learn" the parameters a little bit and so not run so well after a battery disconnect? Also I assume it runs worse now as after reset the car hasn't distinguished the dodgy sensor yet (no EML on) and so is not ignoring it (or whatever it does when it goes into EML failure mode)?

Have I understood correct or is there another reason why a battery disconnect might cause it to run different?

TIA
 

LostKiwi

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Over time any electronic fuel injected petrol car will learn the fueling adjustment required for clean running. These are visible as short and long term fuel trims when reading the actual values using OBD2 readers. A long battery disconnect can reset these on some cars.
 
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d215yq

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Valencia, Spain
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1987 W124 300D 280k miles
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Thanks, it started running better after 50 miles and the light stayed off too enough for an MOT pass and emissions were well within range too. I expect it will come back on at some time but not really an issue until next year.
 
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