# Rough idle and misfire from cold start



## VeeDubyaJetta (Jun 28, 2007)

Just got a Jetta again - 2010 Limited Edition just shy of 100K miles and I've got one problem with it. From a cold start, usually in the morning, the 1st 10-15 seconds run rough before settling down to idle. Most of the time it comes with a code for a cylinder 1 misfire but not every time. Previous owner apparently had the same issue as there was an aftermarket coil pack in cylinder 1, which I replaced with an OEM coil pack along with replacing all the spark plugs with OEM Bosch. Still happening.

Any suggestions?

Thanks,
Dave


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## Ark83 (Apr 26, 2012)

the first few seconds of startup is when the secondary air injection occurs. Maybe its something to do with that system.


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## kevin splits (Aug 23, 2010)

Sounds like a n80 valve


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## Dave558 (Aug 9, 2010)

Mine does this occasionally too, in fact just posted about it yesterday since the issue seemed to be a bit more extreme than usual. Thankfully the occurrence is rare enough still. 

In your case though when you start it up do you give it a second with the key in the accessories position or do you immediately just go to a quick start? Just curious if a quick start in your situation causes the rough idle/misfire more frequently.


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## mabbonizio186 (Oct 15, 2006)

see my thread.. similar issue, fixed permanently with a software update -- http://forums.vwvortex.com/showthre...o-when-the-VW-dealer-refuses-to-trouble-shoot


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## VeeDubyaJetta (Jun 28, 2007)

*Still fighting the same issue*

Just wanted to update this issue. So far I have replaced the coil pack in cylinder 1, which is primarily where the misfires code to (sometimes I'll get cylinder 5 or random misfire also), all new OEM spark plugs, N80 valve and fuel filter. Still having the same thing happen, though the MIL light now flashes every time while the idle is rough instead of intermittently.

Now the fuel primer pump (? - the one that turns on when you open the driver's side door after sitting for a while) is getting louder and harsher sounding when it turns on. Doesn't matter if I turn the key immediately or first to the ACC position for a few seconds before starting. Saw a few other threads that mentioned the PCV valve so thinking about trying that next but with the fuel primer sounding worse every day want to see if that could be related or something different.


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## Ronny Bensys (Apr 17, 2014)

Why not reading CEL with vagcom or any Torque like app?

PCV valve is fully closed at start-up so it has nothing to do with cold start logic.


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## VeeDubyaJetta (Jun 28, 2007)

Ronny Bensys said:


> Why not reading CEL with vagcom or any Torque like app?
> 
> PCV valve is fully closed at start-up so it has nothing to do with cold start logic.



I have been reading the codes and clearing them with a U-Scan ODB Bluetooth connector and software on my phone. 

Still happening, forgot to mention that on occasion I also have Gas Cap errors show up in the dashboard as well as P0455 codes for Evap Emission System Leak Detected. Like the Cylinder 5 misfire (P0305) and Random Multiple Misfire (P0300) codes, they do not happen every time the light comes back on after I do an ODB code reset. The only one that is a constant is the P0301 Cylinder 1 misfire.

I have also had an issue with brief losses of power at highway speed but they seemed to happen only when I was around 1/4 tank of gas and I haven't had any since replacing the fuel filter 2 weeks ago. Other than that happening maybe 3-4 times tops, the only time I have rough idle is still the first 10-15 seconds after a cold start.


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## VeeDubyaJetta (Jun 28, 2007)

*Also replaced PCV valve...*

Oh yeah, I also replaced just the PCV valve with the Dorman PCV diaphragm repair kit. The rubber gasket/diaphragm did have a slice in it but I can't be sure that I didn't do that trying to get the dang thing off.


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## Ronny Bensys (Apr 17, 2014)

It seems you got success narrowing down the problem by just throwing money randomly where fuel runs.  So you have only fuel pump left. But before going for more into pocket, there might be a method for measuring fuel line pressure.


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## altoba (Dec 5, 2010)

Did you ever find out the root cause of the problem. I am having the same issue. Cylinder 1 misfires when I first start after a long time (like in the morning or after work). I turn the car off for a couple of times and then it fires perfectly every time.

Thanks in advance,
Alfonso
2009 2.5 Jetta (145kmi)


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## Ronny Bensys (Apr 17, 2014)

Cylinder 1 misfires not always because it's malfunctioning. Some other components participating in cold start not running properly. This can be fuel system, EVAP components, dirty manifold, vacuum leaks, bad battery etc.

I'd recommend first testing N80 valve as it is a wide-spread and well-known culprit in our engines. Second point is to check if fuel pump is running or not when key-on. If these are ok and you are handy with tools then remove engine cover, coils and observe spark plugs wells using good source of light. If you see any signs of water, oil or rust inside the well then you are at the point. Otherwise, if everything is ok, I would stop at this step and head to mechanic for further inspections.


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## altoba (Dec 5, 2010)

Ronny Bensys said:


> Cylinder 1 misfires not always because it's malfunctioning. Some other components participating in cold start not running properly. This can be fuel system, EVAP components, dirty manifold, vacuum leaks, bad battery etc.
> 
> I have already swapped the spark plugs and coils and the problem persists. I have not checked the N80 valve, neither have I looked inside the spark plug well. I will do that this weekend and report. The times that I have removed the cover to look at the spark plug or coils, the car works fine for a day or so, then the problem comes back again.


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## Ronny Bensys (Apr 17, 2014)

After engine starts and revs to make secondary injection pump do its job, N80 valve must open to purge charcoal accumulated vapors to intake manifold. But if N80 valve is stuck open, it releases all remaining vapors from EVAP line to manifold, slowly accumulating over night or longer periods while car sits in the garage. To check it, you can simply press EVAP hose before N80 and keep it like this with a pump pliers like tool over night or so. Next day start the engine like this and see if it makes any difference. You might need several days to make sure N80 valve is not the case here but it worth doing the test since the result will certainly save some money.


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## altoba (Dec 5, 2010)

Tried your tip on the n80 valve and it seems it is not the culprit, I was hoping though. Since I had a set of new spark plugs, I replaced them yesterday and the car has been running a lot better. But it always does when I take things apart and re-assemble. We will see this coming week. I did noticed that my coolant level was a little low, so I am afraid that there may be some tiny leakage into cylinder #1 since I keep getting the PO031 code. The saga continues, any inputs and comments are welcome and appreciated.


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## Ronny Bensys (Apr 17, 2014)

From your posts what I understand you have replaced plugs twice in short intervals and after every change you found the engine running better. Did you inspect the "old" plugs? How they look? Any signs of rust or oil?


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## [email protected] (Oct 26, 2012)

It seems possible that you could have a bad VW 2.5 Fuel Injector if it is only really happening on one cylinder it very unlikely to be fuel pump related. You also should contact your local dealer about the software update as mentioned above. If that is available on your vehicle you should start with that.


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