Rough idle on a Seat Leon Cupra 300 4drive

Aug 8, 2024
6
1
Hungary
Hello everyone!

2 days ago I purchased a Seat Leon Cupra 300 4drive with the DSG6 gearbox. Since I'm waiting on some paperwork, I was unable to test drive the car (I drove it before with the previous owner's plate before purchasing). Before continuing to describe the problem, do note that I've never owned an automatic car nor DSG, and this is my first petrol-powered car. I have a manual 2.0 pre-facelift 110kw diesel, which runs extremely smoothly on idle even when it's cold.

The car runs rather rough when starting up, it starts quickly, no problems with that. But it starts vibrating for brief moments, the revs drop, then increase (between 600-1000 rpm) and the exhaust sounds different when these rpm-drops occur. Until the oil temperature reached 80 degrees, the car felt very shaky and jerky (was sitting inside the whole time monitoring the situation), after the oil reached 80 degrees celsius, the shaking stopped and the revs stabilised around 680-710. However, according to my OBD device, the coolant water went above 95 degrees celsius (the dashboard reading remained steady at 90), and this is what concerns me the most. I revved the engine once to 3000 rpm, but after that the rpm's remained steady during idling. No DTC's and according to my device, the last DTC was cleared 65500 km ago (car has 170k).

The car has a digital service book, oil changes every 10-20k kms, DSG, and Haldex oil replaced 40k km ago, so it's still between the regular intervals. Coolant level (when cold) was well over the minimum mark, but below the maximum by an inch or two. The oil level was also between the markings, slightly lower. The oil filler cap is completely clean, and so is the coolant expansion tank cap. I mean, the reason I bought the car because it was maintained at the very same workshop since its first kilometres, and the owner was the original owner who bought it in 2017. No stage 1 or any modifications to the engine, however the previous owner was running a Hurricane V2 exhaust, but the car was never tuned (i believe him). Gearbox isn't mapped, in normal mode, it does shift up around 1900-2000 rpm.

The car was in PARK for the whole process. Please help me ASAP, because I am really doubting my purchase right now.
 

nd-photo.nl

Active Member
Mar 6, 2012
4,489
542
The Netherlands
youtube.com
Can you scan for misfires? Also check fuel trims & maybe also inspect the spark plugs. When was the last time they were swapped out with new spark plugs?

I have an ST280 with the DSG6 (aka DQ250), which is more or less the same car. On cold start it will idle a bit higher to heat up the cat as soon as possible, before dropping down in rpms a bit. I think this takes (over) a minute, before dropping down in revs for normal idling.

Coolant temps will always fluctuate, but I havent done the comparison between OBD and what is on the screen. Normally the dashboard will keep pointing at 90 degrees while the coolant temp is fluctuating as the thermostat opens and the cooling system does it job. This cycle is repeated off course.

I think the jerkyness has to do with ignition or some airleak. Thats why I am asking about misfires and fuel trims
 
Adrian Flux insurance services - discount for forum members.