Engine shakes and nearly stalls

[nimas1377]

Hi so I have a 2017 mirage with 1.2L engine and CVT transmission and I was wondering if the behavior I’m experiencing is normal

So when I use the car specially when it’s warm and the idle rpm is low the car when for example stop in a parking lot and moving with no acceleration and just controlling with brakes sometimes stars to shake and rpm drops really low ( specially when there is a load from electrical systems) and the lights flicker a bit and the engine sounds like it’s choking exactly like when you drive a manual and you didn’t press the clutch enough and engine starts to shake and sound like it’s choking. Btw the car never stalls and the change in vibration and the sound is annoying but not if it’s normal

I should note that the problem never happens with ac but when ac compressor goes off it shows again and when the compressor kicks in it fixes
And another note that I mostly used this car with the ac on even in winter for better defrosting so maybe the idle logic of the car is badly calibrated to my usage
So is it normal and if not how can I fix it?
Thanks in advance

[7milesout]

nimas - That's not normal on your car. By your description, it is idling too low. I'm not sure all cars, but most cars are programmed to pick up a bit of rpm when the A/C compressor kicks on.

Here's what I estimate is happening. The bump in rpm causes it to idle more smoothly. And when not using the A/C, the rpm drops too low and the engine is just not balanced very well at that low rpm. But what's causing the low rpm?

I'll tell you what caused the almost identical symptoms as you describe, on my 2003 Toyota Camry. A dirty throttle body. In case you don't know (maybe you do), a throttle body is more or less a tube with a butterfly valve in it. Said valve is controlled by the ECU in our car, and indirectly by your right foot. You push the throttle, the butterfly opens some amount to increase airflow to the engine. At idle, that butterfly is very close to being closed. It only allows a small amount of air to pass by. Just enough air flow to idle the engine at the proper AFR.

In that Camry, I pulled that throttle body out and wow, it was coated with schmutz exactly where air flowed around that butterfly valve at idle. And on the edges of the butterfly where the air flowed past it at idle. I took a toothbrush, paper towels and throttle body cleaner (spray) and sprayed and cleaned that throttle body until it was as clean as possible. Nearly new looking. I put it back in the car and MAN, what a difference. No low idle, perfect throttle response easing away from a stop. It was like the car was new again. All that build up was restricting airflow at idle, and causing the engine to idle low. And at that lower than target idle rpm, the engine wasn't balanced well, and it vibrated badly. All that was gone after I cleaned it.

I'm not saying that's the issue with your Mirage. But the symptoms sound very similar.

[Fummins]

Hi so I have a 2017 mirage with 1.2L engine and CVT transmission and I was wondering if the behavior I’m experiencing is normal

So when I use the car specially when it’s warm and the idle rpm is low the car when for example stop in a parking lot and moving with no acceleration and just controlling with brakes sometimes stars to shake and rpm drops really low ( specially when there is a load from electrical systems) and the lights flicker a bit and the engine sounds like it’s choking exactly like when you drive a manual and you didn’t press the clutch enough and engine starts to shake and sound like it’s choking. Btw the car never stalls and the change in vibration and the sound is annoying but not if it’s normal

I should note that the problem never happens with ac but when ac compressor goes off it shows again and when the compressor kicks in it fixes
And another note that I mostly used this car with the ac on even in winter for better defrosting so maybe the idle logic of the car is badly calibrated to my usage
So is it normal and if not how can I fix it?
Thanks in advance

It's hard to figure out exactly what your car is doing, might be normal or maybe not. How low does the rpm go? Nearly stalling wouldn't be considered normal. Does it only act this way while in drive(or reverse)?
The sound could be anything from a rattling air cleaner(or snorkle) to exhaust heat shield? Could be the belt or a combination of any of them?

I've got a car waiting to come into the shop that vibrates badly when in drive or reverse(I can't remember which), I'm positive its problem is caused by gravel and crap jammed in the suspension cross member (/k-frame/subframe)and wedged behind the one engine mount.

Are you able to post a clip of what you're seeing and maybe the tach when it's acting up?

Have you ever had the cvt serviced(fluid replaced), just for sharts how does the fluid look? If it's black then you might have issues there.

[nimas1377]

nimas - That's not normal on your car. By your description, it is idling too low. I'm not sure all cars, but most cars are programmed to pick up a bit of rpm when the A/C compressor kicks on.

Here's what I estimate is happening. The bump in rpm causes it to idle more smoothly. And when not using the A/C, the rpm drops too low and the engine is just not balanced very well at that low rpm. But what's causing the low rpm?

I'll tell you what caused the almost identical symptoms as you describe, on my 2003 Toyota Camry. A dirty throttle body. In case you don't know (maybe you do), a throttle body is more or less a tube with a butterfly valve in it. Said valve is controlled by the ECU in our car, and indirectly by your right foot. You push the throttle, the butterfly opens some amount to increase airflow to the engine. At idle, that butterfly is very close to being closed. It only allows a small amount of air to pass by. Just enough air flow to idle the engine at the proper AFR.

In that Camry, I pulled that throttle body out and wow, it was coated with schmutz exactly where air flowed around that butterfly valve at idle. And on the edges of the butterfly where the air flowed past it at idle. I took a toothbrush, paper towels and throttle body cleaner (spray) and sprayed and cleaned that throttle body until it was as clean as possible. Nearly new looking. I put it back in the car and MAN, what a difference. No low idle, perfect throttle response easing away from a stop. It was like the car was new again. All that build up was restricting airflow at idle, and causing the engine to idle low. And at that lower than target idle rpm, the engine wasn't balanced well, and it vibrated badly. All that was gone after I cleaned it.

I'm not saying that's the issue with your Mirage. But the symptoms sound very similar.

Thanks for the reply. The car is relatively new with only 30K km on it and I actually showed the car to a mechanic near my house and he cleaned the throttle body with spray but idk how good of a job he did.

But I will check the throttle body again

[7milesout]

In my opinion, spraying it with spray is not very helpful. Spraying it with spray, and toothbrushing it when wet with the spray to loosen it, spraying it again and wiping it out with a towel is the way to go in my opinion.

[nimas1377]

It's hard to figure out exactly what your car is doing, might be normal or maybe not. How low does the rpm go? Nearly stalling wouldn't be considered normal. Does it only act this way while in drive(or reverse)?
The sound could be anything from a rattling air cleaner(or snorkle) to exhaust heat shield? Could be the belt or a combination of any of them?

I've got a car waiting to come into the shop that vibrates badly when in drive or reverse(I can't remember which), I'm positive its problem is caused by gravel and crap jammed in the suspension cross member (/k-frame/subframe)and wedged behind the one engine mount.

Are you able to post a clip of what you're seeing and maybe the tach when it's acting up?

Have you ever had the cvt serviced(fluid replaced), just for sharts how does the fluid look? If it's black then you might have issues there.

The rpm goes to about 500-550 or maybe lower I didn’t look to close I just saw it drops.

I notice it the most while in drive or reverse cause when you put the car in N the rpm clime a bit

The sound isn’t really bad it is exactly like when you drive a manual and you for example start in 3rd gear and engine can’t hold on and rpm drops and engine shakes so I’m not really worried about the sound.

I will record it next time and upload it to google drive for you to hear and see it

The car is at 31K km and I’m planning to change the cvt oil and filters at around 36-37K with my next oil change and the fluid is green with a bit of metal dirt in it and not fully black yet ( I don’t think there is anything wrong with the fluid - it seems pretty clean )

[nimas1377]

In my opinion, spraying it with spray is not very helpful. Spraying it with spray, and toothbrushing it when wet with the spray to loosen it, spraying it again and wiping it out with a towel is the way to go in my opinion.

Yeah I will show it to a different mechanic, do you think with only 31K it is really the throttle body?

[Fummins]

The rpm goes to about 500-550 or maybe lower I didn’t look to close I just saw it drops.

I notice it the most while in drive or reverse cause when you put the car in N the rpm clime a bit

The sound isn’t really bad it is exactly like when you drive a manual and you for example start in 3rd gear and engine can’t hold on and rpm drops and engine shakes so I’m not really worried about the sound.

I will record it next time and upload it to google drive for you to hear and see it

The car is at 31K km and I’m planning to change the cvt oil and filters at around 36-37K with my next oil change and the fluid is green with a bit of metal dirt in it and not fully black yet ( I don’t think there is anything wrong with the fluid - it seems pretty clean )

I can't remember what normal rpm is while in drive stopped? I asked about the fluid cause I've had a few cars almost stall when pulling up to a stop. The problem with them was a bearing inside the cvt piling up and stalling out the engine. With only 30k I doubt that's your problem but if you bought the car used it's possible the mileage has been altered. It's easy to replace the speedometer cluster with one from a lower mileage car, can be done in under a minute.

[nimas1377]

I can't remember what normal rpm is while in drive stopped? I asked about the fluid cause I've had a few cars almost stall when pulling up to a stop. The problem with them was a bearing inside the cvt piling up and stalling out the engine. With only 30k I doubt that's your problem but if you bought the car used it's possible the mileage has been altered. It's easy to replace the speedometer cluster with one from a lower mileage car, can be done in under a minute.

I really doubt if the mileage has been changed because the car body was at the time of purchase in perfect condition back then but it can be the throttle body as what 7milesout said. also now that you said it might be changed I hear a sound when crossing a speed bump it's like a plastic sound but happens really often when going on bumps specially in cold days can that indicate that the car isn't as new as it says?

[Fummins]

It's hard to say...It seems like there are always different parts that wear out in different parts of the world.
How it was used plays a big part too.