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I had a hair-raising incident yesterday. My engine (automatic transmission) cut out while driving at around 30mph on a main road, just like a manual stalling. It restarted on the first attempt as soon as I'd realised what was happening, after putting it into parking gear etc.

After this, it drove but struggled to shift itself above second gear and struggled to accelerate. If I accelerated a normal amount, the revs would lurch and bounce up and down alarmingly without the car gaining speed like it was stuck bouncing between gears. I put it into "2" and drove slowly, and it seemed better, but even then the revs occasionally went up or down for a moment with no obvious reason.

I was down to about 20% fuel, and this is a country where fuel quality can be low (sometimes literally watered down). I crawled along to a petrol station and refueled - after refueling, it was a little slow to accelerate at first especially going up hill, but after about 15 minutes on the road seemed pretty normal.

After letting everything cool down, I checked transmission fluid levels*, and they were normal. No problems at all shifting between positions on the PRND2L stick, either - reverse reversed, park parked, drive drove, 2 and L behaved as expected.

Could what happened be explained by low / bad fuel or should I do other checks as well?


*oops, I should have checked transmission fluid while the engine was idling, not after letting it cool down (according to the Haynes manual for this car and model). Actually, my transmission fluid was low - topped up now.

  • This is the RAV4, right? – Zaid Aug 13 '16 at 10:33
  • Haha, yes :-(. But despite the 25 questions that old banger has prompted now, it's still in better shape than most cars on the road here... – user568458 Aug 13 '16 at 11:38
  • Transmission fluid level can change a lot depending on temperature. Does your owner's manual call for checking the level with the engine idling? Does your dipstick have a hot level mark and/or cold level mark? – Zaid Aug 15 '16 at 12:35
  • @Zaid The Haynes manual for this car says to do so with the engine idling. Weirdly the Owner's Manual doesn't specify (it has every other type of fluid, but for transmission fluid it only says to check the transmission fluid temperature indicator). The transmission fluid level was well below both the hot and cold indicators with the engine running at idle – user568458 Aug 15 '16 at 12:53
  • Ok, just making sure the level really was below par – Zaid Aug 15 '16 at 12:54
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What you have described are classical symptoms of what happens when a bad batch of fuel finds its way inside an engine - sputtering/coughing/misfiring during low-load operation.

If the issue recurs with fuel that is known to be good, another possibility is that the fuel supply system is unable to deliver the required amount of fuel, causing the engine to misfire. Things to check in such a situation would include:

  • a clogged fuel filter
  • a malfunctioning fuel pressure regulator
  • a weak fuel pump

Symptoms of fuel starvation usually manifest themselves under high-load situations, so sudden acceleration, going uphill and high speed travel will all be cases in which the engine could misfire in case of inadequate fuel supply.

  • So basically, if it functions well now it's got a full tank, it's probably okay? Also assuming that the last 20% in my tank is bad, should I take any steps to clear it out? – user568458 Aug 13 '16 at 11:40
  • @user568458 that's your call. The only practical way to know if you really needed to purge the fuel system of the bad fuel is by using it :) – Zaid Aug 13 '16 at 18:42
  • Update: I've driven it about 140km since asking this question, including asking a mechanic to drive it up the steepest hill in town to judge if the transmission and acceleration feel and sound how they should, and it performed perfectly fine, so I'm pretty confident it was just the bad fuel and will leave things as they are and just remember to not let the tank drop below 25% in future. – user568458 Aug 15 '16 at 12:23

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