This is an article about an unexplained idle surging with the G4FJ engines that are common in Kia and Hyundai vehicles (Kia Cee’d GT, Hyundai i20N…), it’s a 1.6 turbocharged (1.6 T-GDI) engine that produces 204 PS engine power and a little less than 300 Nm of torque.
Please if you have any information about this, leave a comment below, so we can get to the bottom of this. Thank you!
So the issue is: unexplained idle surging (vibrations can be felt through the vehicle, most commonly through the seat and the floor). The idle surging appears only SOMETIMES, and not always, which is extremely hard to diagnose. It also doesn’t matter the outside temperature… The electrical components don’t make the issue worse/better. The issue appears around 700 RPM on idle.
What has been tried:
- AC on/off, seems to be better if the AC is on, but that is only because it makes the revs go higher.
- Lights on/off, doesn’t matter,
- Internal light on/off, doesn’t matter,
- Internal blower doesn’t affect it, even if you turn it off, the issue persists.
What has been investigated:
- Sparkplugs are from Bosch and are pretty new,
- Valves inspected with endoscope – there is a little bit of carbon on the direct injectors and valves but not much.
- Battery was changed,
- Changed PCV valve,
- Cleaned the throttle body a bit (there was a bit of carbon on the start).
What we found out:
The issue usually doesn’t appear if you let the car get through the cold start program (it idles loudly at 1500 rpm and after some time it goes down to 1000 rpm). So this is something that might work. Start the car and let it idle for 2 minutes. The problem is, when you start it again (when it’s hot) the issue usually reappears.
ALSO: prime the fuel pump always. That means when you want to start the car:
- Sit inside the car and close the door,
- Press the start button once (without pressing the clutch),
- Press the start button second time (still without pressing the clutch),
- Wait a bit (few seconds so everything primes),
- Then press the clutch fully and start the car
Observations:
19. 03. 2024
The car was started in the morning and let the cold start till the end (car was idling for about 4 minutes on cold start) then a normal commute happened (about 30 minute drive, not much stopping, hard on gas for highway…), then we got to the parking garage the car sit still and there were still vibrations… Even with lights off, ventilation off, still…
Back going home, we turned off ventilation before starting the cold start. It was better on red lights, but still some vibration was felt. Then another start happened (warm start) and it was rough idle as usual. We even got a recording of the idle from Torque Pro:
As we can see it goes from 692 RPM to 709 RPM, this is why vibration is felt. Further inspection will be needed…
Also good thread I found today: Uneven tickover at idle | Kia Owners Club Forum
22. 03. 2024
Today I drove the car and found out that it doesn’t even matter if the A/C is on, ventilaton… it is still vibrating. The only thing that changes is the vibration interval. So if we interpret the vibrations with a graph:
= normal idle
! vibration
Without ventilation and A/C:
===== ===== ===== ===== ===== ===== ===== =====
!! !! !! !! !! !! !!
With ventilation and A/C:
=== === === === === === === ===
!! !! !! !! !! !! !! !!
So as you can see, the vibration changes with RPM, meaning higher RPM, the faster the interval of vibrations.
25. 03. 2024
I have found somewhere in the comments that the idler pulley could be the issue. Mine has a bit of play in it. Maybe this is the culprit of this issue. I will try to change it or notify my mechanic to see his reaction.
24. 10. 2024
Another thing that I found that might be worth a try:
19. 11. 2024
Changed the sparkplugs and two coils as they were faulty. The idle surging still remains…