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Old 10-18-2020, 09:12 AM   #1
Drives: Toyota Yaris
Join Date: Jan 2015
Location: Australia
Posts: 3
Engine stalling in very hot weather

Our 2008 4sp automatic 1.5l Yaris sedan stalls intermittently or loses power at low rpm in very hot weather (>35C). Car has 150k kms and has been doing it since around 80ks. Car is completely stock.

The most common set of circumstances is after car has a long period of idling or lots of stop/start driving or slowing down after a long period of highway driving. It starts again immediately with no issues. If temperature is less than 35C then doesn't seem to be an issue.

No engine codes have been recorded. Fuel filter in the tank has been replaced recently and resulted in no change. Throttle body has been cleaned. Spark plugs replaced. Car uses E10 fuel.

To my inexperienced mind it seems like it may be a vapour lock although it does not appear to be related to amount of fuel in the tank.

Another (possibly unrelated) symptom is that when driving with a very light throttle setting in a 50kph zone, the rpms seem to randomly drop for a fraction of second from 2000 to 1000 rpm and then back up to 2000rpm. This symptom happens at any outside temperature (hot and cool weather). The drop is so short that you barely notice in terms of the cars driving but you can see it on the tacho.

Any help would be much appreciated!

Last edited by serendipity; 10-27-2020 at 01:26 AM.
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Old 10-18-2020, 05:59 PM   #2
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Drives: 2013 NCP130
Join Date: Nov 2015
Location: Sydney, Australia
Posts: 292
I can't comment on the stalling problem, but the momentary rev drop at very light throttle may be normal operation due to the 'drive by wire' throttle contol.

The accelerator pedal is merely an electronic input to the ECU. The rev drop occurs at very light throttle when the pedal is very close to idle. The ECU can't determine whether the throttle should be open or not, and wavers a bit between throttle on and idle. It does not happen when using the cruise control, as the pedal idle position is ignored, and the ECU operates the throttle to maintain the set speed.
Running on standard AU 14" steel wheels (14x5 rims, 175/70R14 tyres). Added reversing camera and touch screen radio, cruise control, 16" rear wiper blade, tow bar and dash cam.
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Old 10-19-2020, 08:46 AM   #3
Drives: Toyota Yaris
Join Date: Jan 2015
Location: Australia
Posts: 3
Thanks very much, that's a very clear (and likely) explanation on the rev. wavering. Sadly, almost certainly not related to the stalling though.
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Old 10-19-2020, 08:20 PM   #4
2ZR swap. DO IT! Ask how!
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Drives: 09 Meteoric Metallic HB
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Location: West Michigan
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Please only start one thread per issue.
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