slandi
12-02-2025, 02:24 PM
Hi everyone,
So I picked up my 2012 Yaris Sedan LE with automatic transmission with 57,000 Km on it. She's really clean and, I kid you not, previously owned by a little old lady who only drove it to church and to the grocery store.
The car looks great, the engine starts up right away and idles well. My problem is if I stick to a constant speed of say around 40 Kph and just feather the throttle keeping it around 1,500 RPM, every now and then I see the RPMs dip by about 500 and the engine feels like it's misfiring. I checked the OBD and there are no codes, no misfire codes, nothing. It does this intermittently and only seems to do it when the engine is warm or at operating temps. I thought at first it might be my transmission hunting for 3rd to 4th but when I place it in 3rd, it still does it a bit, though a bit less.
Now, judging by the fact that the previous owner bought it in 2012 and, I hate to be morbid about this, but by her passing away in late 2020, had only put about ~50,000Km on it, I'm thinking the car may have sat unused during the estate settlement, perhaps several years.
So, now I'm thinking could it have been bad gas, I put in a full tank back on Monday Nov 24th and unfortunately got terrible consumption that first week of something like 9Lt/100Km (26mpg). Yes, mostly city driving, but honestly was hoping for better.
Then I questioned maybe the air filter, but I found all the service records for the car, including dozens of oil changes at the same garage, so she was meticulous with the maintenance, however I noticed that the air filter was never mentioned once in those oil changes. So I went out and took out the air filter and I swear it was probably the original air filter. So out it came and in went a new one, hoping that might have been the problem, but the slight hesitation and seemingly misfiring persists.
Then I started thinking maybe it's the fuel injectors, given that the car may have sat somewhere, possibly for years, could the fuel injectors have been gummed up or something with bad gas, does that even make sense? The car accelerates well, idles well and under both acceleration and driving at higher speeds >80 Kph does not exhibit the 'supposed' misfiring.
I also thought maybe it's the Accelerator Pedal Sensor, I thought perhaps it was a potentiometer type arrangement and so maybe the contact near the top travel of the pedal, where I'm just feathering it, might be oxidized and not making proper contact and sending an erratic signal to the ECM. However, when I read up on those sensors, most of them use Hall Effect Sensors, so not actual brushes/contacts to get contaminated. Does our Yaris' use those type of sensors, I think so? Also, I'm thinking if this was the case, then the idle would show the same loss of RPM no?
My next step is to pull the plugs and see if perhaps they might be bad because I imagine if the air filter had been clogged for 57,000Km perhaps it was running too rich and possibly fouling the plugs. Again, though I figured the computer would adjust the fuel in ratio to the air, and thus, hopefully, run the mixture neither too lean or rich, does that make sense?
Finally, I didn't want to just start changing parts randomly to see what will work. Changing air filter, plugs and maybe injector cleaner (if that even works) is on my agenda right now.
Perhaps the car just needs to run for some time, get some miles on her, let the fuel system kind of clean itself out.
I welcome any insights on this, has anyone else exhibited this type of behaviour on their Yaris?
I'll try and post a video perhaps when I catch it happening but again it's intermittent and so can be a bit tricky, though when it does happen, it will do so for quite some time.
Thanks for reading this far. :)
So I picked up my 2012 Yaris Sedan LE with automatic transmission with 57,000 Km on it. She's really clean and, I kid you not, previously owned by a little old lady who only drove it to church and to the grocery store.
The car looks great, the engine starts up right away and idles well. My problem is if I stick to a constant speed of say around 40 Kph and just feather the throttle keeping it around 1,500 RPM, every now and then I see the RPMs dip by about 500 and the engine feels like it's misfiring. I checked the OBD and there are no codes, no misfire codes, nothing. It does this intermittently and only seems to do it when the engine is warm or at operating temps. I thought at first it might be my transmission hunting for 3rd to 4th but when I place it in 3rd, it still does it a bit, though a bit less.
Now, judging by the fact that the previous owner bought it in 2012 and, I hate to be morbid about this, but by her passing away in late 2020, had only put about ~50,000Km on it, I'm thinking the car may have sat unused during the estate settlement, perhaps several years.
So, now I'm thinking could it have been bad gas, I put in a full tank back on Monday Nov 24th and unfortunately got terrible consumption that first week of something like 9Lt/100Km (26mpg). Yes, mostly city driving, but honestly was hoping for better.
Then I questioned maybe the air filter, but I found all the service records for the car, including dozens of oil changes at the same garage, so she was meticulous with the maintenance, however I noticed that the air filter was never mentioned once in those oil changes. So I went out and took out the air filter and I swear it was probably the original air filter. So out it came and in went a new one, hoping that might have been the problem, but the slight hesitation and seemingly misfiring persists.
Then I started thinking maybe it's the fuel injectors, given that the car may have sat somewhere, possibly for years, could the fuel injectors have been gummed up or something with bad gas, does that even make sense? The car accelerates well, idles well and under both acceleration and driving at higher speeds >80 Kph does not exhibit the 'supposed' misfiring.
I also thought maybe it's the Accelerator Pedal Sensor, I thought perhaps it was a potentiometer type arrangement and so maybe the contact near the top travel of the pedal, where I'm just feathering it, might be oxidized and not making proper contact and sending an erratic signal to the ECM. However, when I read up on those sensors, most of them use Hall Effect Sensors, so not actual brushes/contacts to get contaminated. Does our Yaris' use those type of sensors, I think so? Also, I'm thinking if this was the case, then the idle would show the same loss of RPM no?
My next step is to pull the plugs and see if perhaps they might be bad because I imagine if the air filter had been clogged for 57,000Km perhaps it was running too rich and possibly fouling the plugs. Again, though I figured the computer would adjust the fuel in ratio to the air, and thus, hopefully, run the mixture neither too lean or rich, does that make sense?
Finally, I didn't want to just start changing parts randomly to see what will work. Changing air filter, plugs and maybe injector cleaner (if that even works) is on my agenda right now.
Perhaps the car just needs to run for some time, get some miles on her, let the fuel system kind of clean itself out.
I welcome any insights on this, has anyone else exhibited this type of behaviour on their Yaris?
I'll try and post a video perhaps when I catch it happening but again it's intermittent and so can be a bit tricky, though when it does happen, it will do so for quite some time.
Thanks for reading this far. :)