I20 warm engine idle stall - Hyundai Forums : Hyundai Forum
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post #1 of 36 (permalink) Old 03-12-2019, 02:31 AM Thread Starter
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Hi all, so I have this fairly clear idle stall problem on my petrol automatic i20.
First off I changed the air filter, all igniter plugs, oil filter, cleaned the throttle body.....
The engine starts perfect when cold and isles at 1000rpm..... as the engine slowly warms up the idle gets rougher and rougher until it sits around 600rpm spluttering around..... any higher revs are perfectly fine and the engine accelerates perfectly but when the revs come down the engine stalls. With a warm engine it will not hold idle, especially when the revs come down from a higher range....
I’m getting a obd2 reader today to see if there are and faults flagged but so far I have no engine lights or any other anomalies apart from the engine stalling.
Yes one thing but I doubt it is of consequence, the car battery is old and weak and I need to replace it.
Any suggestions what could be the cause? Or approach to find the cause? Throttle air control valve? Crank sensor? I’m not sure since it drives fine when warm, no problem with power, just the idle won’t hold

Last edited by Nudlaug; 03-12-2019 at 02:42 AM. Reason: Forget a few details
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post #2 of 36 (permalink) Old 03-12-2019, 12:59 PM
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Quote:
Originally Posted by Nudlaug View Post
Hi all, so I have this fairly clear idle stall problem on my petrol automatic i20.
First off I changed the air filter, all igniter plugs, oil filter, cleaned the throttle body.....
The engine starts perfect when cold and isles at 1000rpm..... as the engine slowly warms up the idle gets rougher and rougher until it sits around 600rpm spluttering around..... any higher revs are perfectly fine and the engine accelerates perfectly but when the revs come down the engine stalls. With a warm engine it will not hold idle, especially when the revs come down from a higher range....
Iím getting a obd2 reader today to see if there are and faults flagged but so far I have no engine lights or any other anomalies apart from the engine stalling.
Yes one thing but I doubt it is of consequence, the car battery is old and weak and I need to replace it.
Any suggestions what could be the cause? Or approach to find the cause? Throttle air control valve? Crank sensor? Iím not sure since it drives fine when warm, no problem with power, just the idle wonít hold
Crank sensors are known for failing when hot.






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post #3 of 36 (permalink) Old 03-12-2019, 01:20 PM
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You didn't mentiuon what engine we're working with, but my guess is you have a restricted idle air duct in the throttle body....assuming your engine has one.

Hyundai crank sensors do often fail when they get hot, but when that happens the engine isn't able to restart again until the engine and sensor cool down. That doesn't seem to fit with your symptoms.
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post #4 of 36 (permalink) Old 03-14-2019, 01:56 AM Thread Starter
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Ok this took me a while to find out. The engine is a G4FA engine which I believe is 1.4l, petrol.
Yesterday’s OBD2 fault check revealed no codes, no faults.
Real time monitoring showed me very little, rpm stable sa 1000 when started cold, dropping to around 550-600 when warm, running really rough. Ignition timing at that spot was all over the place, jumping by 15 degrees, maybe because it’s trying to compensate for the idle problem? At higher rpm the timing is solid. Oxygen sensor 2 was sitting around 0.6V pretty steady whereas sensor 1 was jumping around from 0.6 to 0.1 and so on, zig zagging. Not sure if that’s normal
But as I said, there are no fault codes flagged.
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post #5 of 36 (permalink) Old 03-14-2019, 02:03 AM Thread Starter
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Thank you for your reply Autospark by the way 🙂
The engine can be started and driven at any temp. Idle stalls usually, or baaaaaaarely splutters along, but even with a hot engine it can still be started and run.
One weird thing though. When I took off the throttle body, to clean it, it had 3 hoses connected to it, 2 were radiator coolant filled, which I found very strange, they seem to hook up to the radiator system though, so seems legit.....
I couldn’t see and blocked idle holes, it seemed to be just a butterfly valve, very clean, no ports or holes to block, as far as I could see anyway 😕
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post #6 of 36 (permalink) Old 03-14-2019, 02:21 AM Thread Starter
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The throttle body says kefico 35100-2B150, I’m guessing this unit is at fault, might as well replace it?
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post #7 of 36 (permalink) Old 03-14-2019, 03:30 AM Thread Starter
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I have uploaded the obd2 real time data to YouTube. The video starts with the engine warming up, rpm can be seen dropping over time and the engine runs rougher and rougher

https://youtu.be/ooh3MyR8FNo
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post #8 of 36 (permalink) Old 03-14-2019, 09:09 AM
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I couldn’t see and blocked idle holes, it seemed to be just a butterfly valve, very clean, no ports or holes to block, as far as I could see anyway
Your engine has an electric throttle so it doesn't have an idle control valve or a idle air bypass duct. Idle speed is controlled by the butterfly valve on your engine.

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Thank you for your reply Autospark by the way 🙂
The engine can be started and driven at any temp. Idle stalls usually, or baaaaaaarely splutters along, but even with a hot engine it can still be started and run.
That kinda rules out a crank sensor fault then,

Quote:
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When I took off the throttle body, to clean it, it had 3 hoses connected to it, 2 were radiator coolant filled
Interesting. I wonder if it might be worth disconnecting the coolant hoses from the throttle body and linking them with a short pipe to see if that makes any difference to how the engine runs as the coolant heats up.

Quote:
Originally Posted by Nudlaug
I have uploaded the obd2 real time data to YouTube.
A couple of things jumped out at me in your video but I'm struggling to understand what is happening. (any thoughts @grcauto?)

The first thing I see is the MAP value looks way too high for an engine at idle. But it seems consistently high throughout the video. I also noticed that the value looked correct when the engine stalled. With the engine stalled (not running) the MAP should show atmospheric pressure (approx 100kpa). Yours shows 98...pretty close, so the sensor itself seems to be OK.

The other thing I see in the video is the high negative fuel trim which suggests the A:F mixture is rich. The output of the O2 sensors don't seem to show a rich mixture though. Have you ever replaced an O2 sensor on the engine?





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post #9 of 36 (permalink) Old 03-14-2019, 11:27 AM
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Your engine has an electric throttle so it doesn't have an idle control valve or a idle air bypass duct. Idle speed is controlled by the butterfly valve on your engine.


That kinda rules out a crank sensor fault then,


Interesting. I wonder if it might be worth disconnecting the coolant hoses from the throttle body and linking them with a short pipe to see if that makes any difference to how the engine runs as the coolant heats up.


A couple of things jumped out at me in your video but I'm struggling to understand what is happening. (any thoughts @grcauto?)


That correlates to 21.785 inches of mercury which is rather high at idle but I'm not familiar with that engine. Also when at 2500 + rpm it's reading 30ish which is very low and it should be a little higher than idle

Something else was the stft were hitting -20 to -25 and the ltft never came off zero.


The first thing I see is the MAP value looks way too high for an engine at idle. But it seems consistently high throughout the video. I also noticed that the value looked correct when the engine stalled. With the engine stalled (not running) the MAP should show atmospheric pressure (approx 100kpa). Yours shows 98...pretty close, so the sensor itself seems to be OK.

The other thing I see in the video is the high negative fuel trim which suggests the A:F mixture is rich. The output of the O2 sensors don't seem to show a rich mixture though. Have you ever replaced an O2 sensor on the engine?





If I were to do the flat rate thing I would throw an O2 sensor in the front and retest. I would leave the map alone at this time.
Before that though......

I would like to see the stft, ltft, #1 O2, map and load all on one screen and do 30 seconds at idle and 30 at 3000 rpm and then a snap throttle. Can you move the PID's around on that tool and put those in the same screen? The snap throttle will likely not yield anything on the tool but......Hey only takes a second.

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post #10 of 36 (permalink) Old 03-14-2019, 12:29 PM
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That correlates to 21.785 inches of mercury which is rather high at idle but I'm not familiar with that engine. Also when at 2500 + rpm it's reading 30ish which is very low and it should be a little higher than idle
Just to make sure we're on the same page :

98kpa KOEO correlates to an atmospheric pressure of approx 28.9"Hg
74kpa at idle correlates to 21.8"Hg, and this is the absolute pressure in the manifold.
To convert from absolute to gauge pressure we subtract the manifold pressure from the atmospheric pressure :
28.9 - 21.8 = 7.1"Hg (gauge). It's been a while since I've used my vacuum gauge but think you would normally expect to see 17~18"Hg if you connected a gauge to the manifold...right?

So something is very wrong with the MAP, like there is a big vacuum leak but that doesn't fit with the negative fuel trim and slow idle speed. On speed density engines vacuum leaks don't usually have much effect on fuel trims since the air leaking in is still being metered, and it usually causes a high idle speed.
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