Hunting Idle on Cold Start??

[Calcoe]

Hi all, this is my first post so apologies if it’s wrong

HUNTING COLD START

I’ve got a 2020 Seat Leon 1.5 MK3.5

Running into a problem with cold starts, does it on a completely stone cold, cold start as well as 45 minutes to an hour it’ll do it too.

Idle hunts, you can hear it in the video I’ve uploaded, on startup, revs increase to a normal 1000/1200, jumps to 1500, back down to 1000 and you can audibly hear the rpms fluctuate. It’s driving me up the wall and I have no idea what to do. I’ve got no fault codes relating to this (warning sign is my front assist out of calibration).

I had an EVAP Fault Code P04401 (I think?), rectified that by getting a new EVAP line and that sorted it. Could this be related in anyway?

Thank you!

 

[mty12345]

EVAP problem can cause hunting idle if drawing through extra fuel. https://wiki.ross-tech.com/wiki/index.php/16825/P0441/001089

Best way to confirm/troubleshoot would be to look at your live fuel trim data while the problem is happening. If you have large negative fuel trims, then very likely it's fuel from the EVAP system being sucked through when it shouldn't be.

P0441 site:forums.ross-tech.com at DuckDuckGo

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[Calcoe]

EVAP problem can cause hunting idle if drawing through extra fuel. https://wiki.ross-tech.com/wiki/index.php/16825/P0441/001089

Best way to confirm/troubleshoot would be to look at your live fuel trim data while the problem is happening. If you have large negative fuel trims, then very likely it's fuel from the EVAP system being sucked through when it shouldn't be.

P0441 site:forums.ross-tech.com at DuckDuckGo

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duckduckgo.com

Hi matey, only problem with that is my EVAP issue has been sorted. I no longer have a fault code for it

 

[mty12345]

Yeah i'm not saying that is the issue, just that there is a chance that the 2 things are related, which was the question you asked lol.

Seeing as you don't have any other fault codes, then checking the N80 EVAP valve is functioning properly is fairly easy and would be the first place i would start. You could have a pending code that will only set after so many cycles. Sometimes fuel vapour can accumulate in the system and intake manifold when the car is sitting, then all be drawn in at cold start.

A large unmetered air leak could also cause high idle, but I can't see any real reason why that would happen at cold start and nowhere else. If it is still idling high when the engine is warm enough to go into closed loop and give you fuel trims, then like i said that would be your easiest way to diagnose it. Large negative trims means extra fuel from EVAP, large positive trims means most likely an air leak.

 

[Calcoe]

Yeah i'm not saying that is the issue, just that there is a chance that the 2 things are related, which was the question you asked lol.

Seeing as you don't have any other fault codes, then checking the N80 EVAP valve is functioning properly is fairly easy and would be the first place i would start. You could have a pending code that will only set after so many cycles. Sometimes fuel vapour can accumulate in the system and intake manifold when the car is sitting, then all be drawn in at cold start.

A large unmetered air leak could also cause high idle, but I can't see any real reason why that would happen at cold start and nowhere else. If it is still idling high when the engine is warm enough to go into closed loop and give you fuel trims, then like i said that would be your easiest way to diagnose it. Large negative trims means extra fuel from EVAP, large positive trims means most likely an air leak.

I got you, yeah sorry I didn’t realise the EVAP issues could rollover if that makes sense? I thought as the code is gone then the problem is gone.

With the N80 valve, that was brand new with the EVAP harness I fitted last year. With the new lines they’re heat wrapped on so I can’t pull the lines off the other end without breaking it unfortunately…

I’ve checked fuel trims during the startup, starts off at -10% and then gradually reduces down to 0% and hovers around there even when driving. Car is tuned, stage 1, but never had this problem until about a year after the tune which wouldn’t make sense, but also being tuned would make sense for extra fuel being pushed.