[trenzterra]

Hi there, I just got a used Hyundai i30 2018 PDE about a month ago. I noticed that occasionally, especially when moving off in slow moving traffic (about 13km/h), I will experience this sudden loss of acceleration where the car speed remains at 13km/h and pressing the pedal down more does not change anything. This happens for about 2 to 3 seconds before power recovers. It is as though the ECU "hangs". I have managed to datalog the latest occurrence this morning (ignore the numbers on the vertical axis) thru Car Scanner Pro and you can clearly see that the RPM and Speed does not respond to pedal input until 2 seconds later.


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I also have a dashcam footage here when it occurs: https://youtu.be/8xgSE8HWSL8?si=pKbIBFbumcL1VCQS

It happens very rarely and intermittently such that when I send it to the workshop, they cannot detect the problem.

Has anyone experienced this before and is there any way to resolve this? Thanks.

[Shambles]

Hi 

My first thought was throttle position sensor (TPS). Any trouble codes (pending/historic) showing in your scanner?

[trenzterra]

Hi 

My first thought was throttle position sensor (TPS). Any trouble codes (pending/historic) showing in your scanner?

Thanks for the welcome! I did a scan and there were no error codes showing. I had the throttle body and MAP cleaned recently though it didn't seem to help things.

I was wondering if it is the throttle position sensor at fault, would I get the graph as shown? Right now it seems that the throttle position increases in accordance with the accelerator pedal, which seems to be expected behaviour. It's just that it does not translate to an increase in RPM.

Digging deeper, I noted from my datalog that the car was stuck in gear 1 for these few seconds, and the "next gear" reading in the OBD scanner changed from 1 to 2 right around when I experienced the issue.

Typically my car tends to shift up to gear 2 at around this speed. Could it be the case that the car somehow couldn't activate gear 2, but not wanting to overrev itself, held itself at the same speed? Though I noted there was a slight dip in RPMs until it "recovered".

[TerryT]

I copied your post to a friend who was very switched on with data logging in our cars when we competed in club level motorsport years ago 

He said he's pretty sure it's turbo lag. Looking at the data, the throttle responds pretty much to the pedal so it's not some built-in dampening of the Drive-By-Wire throttle, and then once it starts to get some air, the rpm responds rapidly.  I think the driver is expecting it to drive like a naturally aspirated (NA) car, but it is a 1.4 ltr turbo.

Something to think about. 

 

[TerryT]

@trenzterra.  I copied your latest reply above to Shambles to my friend and asked for comments.  He replied:

"No, still think it's the turbo catching up, could be something to do with the wastegate sticking , but doubt it.

"It actually only seems to be about a second till it responds to the throttle input, and for the log to be of any more value it would need to be logged at around 0.1 second intervals max, not 1/2 second intervals."

I think that has exhausted his input on the subject but when/if you find out what the issue was it would be nice if you could post on the forum and I will let him know how close or not he was.   

Knowing how good he was with this data logging stuff I suspect I'll be buying the next lunch.

[trenzterra]

@trenzterra.  I copied your latest reply above to Shambles to my friend and asked for comments.  He replied:

"No, still think it's the turbo catching up, could be something to do with the wastegate sticking , but doubt it.

"It actually only seems to be about a second till it responds to the throttle input, and for the log to be of any more value it would need to be logged at around 0.1 second intervals max, not 1/2 second intervals."

I think that has exhausted his input on the subject but when/if you find out what the issue was it would be nice if you could post on the forum and I will let him know how close or not he was.   

Knowing how good he was with this data logging stuff I suspect I'll be buying the next lunch.

Thanks for helping me check on this and on following up! I thought it was turbo lag at first too, but perhaps the data log does not tell the whole story.

So what I am experiencing is that - on a consistent press of the pedal (and not very heavy footed), the car accelerates up to 13km/h but somehow stops accelerating further even though the pedal remains depressed. The feeling is akin to an engine braking feeling.

You can see this at the start of the graph where speed tapers off (the vertical axis numbers are inaccurate as I was trying to fit 4 lines to scale) although accelerator pedal pressure remains consistent. After noticing this (probably about 1 second in?) this is when I try to increase pressure on the pedal, but even doing so the car does not respond at all for about 3 seconds. I noticed also that RPM dips a little bit during this "lag" period.

I corroborated this with my dashcam footage and the lag period seems to be about 3 seconds long. I have experienced this intermittently and each time the lag period is about the same.

99 times out of 100 I do not experience this issue which makes it hard to troubleshoot even at the workshop. On the rare occasion it rears its head, it is normally in heavier traffic (which makes it problematic).

My impression of turbo lag is that it should only last about a second and most and the car should still continue accelerating (slowly?) while waiting for turbo to kick in. But yeah happy to hear if your friend has more insights to share!

[TerryT]

@trenzterra.  I copied your latest post to my friend tonight.  He's a busy guy but he emailed me back saying:

"No idea really, if it is something else [i.e. not turbo lag] and it's happening intermittently then it's going to be hard to diagnose.  Could also be the gearbox, assuming that it's an auto by the rpm vs speed trace."

Sorry, that's all we (he/me) have got. Hope you are able to sort it out.

Cheers,

TT

[trenzterra]

@trenzterra.  I copied your latest post to my friend tonight.  He's a busy guy but he emailed me back saying:

"No idea really, if it is something else [i.e. not turbo lag] and it's happening intermittently then it's going to be hard to diagnose.  Could also be the gearbox, assuming that it's an auto by the rpm vs speed trace."

Sorry, that's all we (he/me) have got. Hope you are able to sort it out.

Cheers,

TT

Thanks a lot. I am getting the dual clutch and actuator replaced in a couple of weeks (have just ordered the parts) since the car is already 100,000km in. Will update you guys it it helps with the issue.

[TerryT]

@trenzterra.  I copied your latest post to my friend tonight.  He's a busy guy but he emailed me back saying:

"No idea really, if it is something else [i.e. not turbo lag] and it's happening intermittently then it's going to be hard to diagnose.  Could also be the gearbox, assuming that it's an auto by the rpm vs speed trace."

Sorry, that's all we (he/me) have got. Hope you are able to sort it out.

Cheers,

TT

Thanks a lot. I am getting the dual clutch and actuator replaced in a couple of weeks (have just ordered the parts) since the car is already 100,000km in. Will update you guys it it helps with the issue.

@trenzterra.  Any update on the problem?

[trenzterra]

@trenzterra.  I copied your latest post to my friend tonight.  He's a busy guy but he emailed me back saying:

"No idea really, if it is something else [i.e. not turbo lag] and it's happening intermittently then it's going to be hard to diagnose.  Could also be the gearbox, assuming that it's an auto by the rpm vs speed trace."

Sorry, that's all we (he/me) have got. Hope you are able to sort it out.

Cheers,

TT

Thanks a lot. I am getting the dual clutch and actuator replaced in a couple of weeks (have just ordered the parts) since the car is already 100,000km in. Will update you guys it it helps with the issue.

@trenzterra.  Any update on the problem?

Changing the clutch helped for a while, but it came back after three weeks. I think it is ultimately an issue with the way the ECU is programmed or something. It seems that there is some delay in rare occasions shifting between gear 1 and 2 although I cannot really find a pattern to reproduce it reliably. Looking through my data logs, it seems the throttle lags behind accelerator input by 1 second, and fuel cuts off momentarily (I'm guessing it's to "protect" the transmission while it attempts to slowly shift up from 1 to 2).

At the same time, I was noticing some minor misfires (not severe enough to trigger a CEL) on Cylinder 4 particularly on a cold start. Im trying to troubleshoot the issue now (initial thoughts point to a fuel injector issue as I've done walnut blasting and also a compression and vacuum leak test to rule out other issues) although I doubt this will resolve the issue.