severe misfire at idle

4.2 V8 40v biturbo - 450 bhp
4.2 V8 40v biturbo - 480 bhp (plus)
stealthyspeeder
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Re: severe misfire at idle

Post by stealthyspeeder » Sat Jul 07, 2012 10:02 am

Ok thanks! now forgive my lack of knowledge but which parameters will I be looking at for the fuel trim? I take it that is not the same parameters as I did originally?

I'll take her out for a spin now and run the orignal log when I get back (damm laptop battery)

No injectors were unplugged, (I hope! as I dont know how to do that imfraid!)

I will check one of the sparks too! Thanks!

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 10:12 am

Log groups 2, 14 and 32. While driving if possible.

Don't reset any DTC.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."


stealthyspeeder
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Re: severe misfire at idle

Post by stealthyspeeder » Sat Jul 07, 2012 11:18 am

Just something I have noticed and thought it was worth taking a video off. At the start the video the car is cold and misfiring like a pig. The Secondary air injection is running is making a bit of a "grindier" noise than it should IMO, but interesting the whole misfiring at idle issue is resolved the second it cuts around 34 seconds in.

Any Ideas what why it would do that?

http://youtu.be/Ong6hYl1VB8

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shpongled
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Re: severe misfire at idle

Post by shpongled » Sat Jul 07, 2012 11:31 am

Bloody hell, just picked my car up from service inc. spark plugs and have exactly the same symptoms as you stealthy, erratic idling in gear with foot on brake, sometimes hesitant pulling away slightly better when up to temperature.... Pulled over to get fuel and the revs ran up to 1600 on idle....

Was going to start a new thread but will keep my eye on this one!

stealthyspeeder
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Re: severe misfire at idle

Post by stealthyspeeder » Sat Jul 07, 2012 11:35 am

I hope its the same issue! I hope its a small issue!

Have you got VCDS? be interesting to see if your getting the same codes a me.

Aslo, is there a massive improvement in your idle once the secondary air intake finished? (or has the car been warm enough not to engage it since you picked it up?)

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shpongled
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Re: severe misfire at idle

Post by shpongled » Sat Jul 07, 2012 11:48 am

Thanks, me too!

I haven't got VCDS so no idea about codes at the mo, I think I need to get that now asap and get up to speed with all that....

I drove it long enough to come up to temperature, about an hour. I pulled off straight away from cold and didn't notice a problem until 3 miles down the road, it hesitated pulling onto a fast roundabout so much I got in the way of some bloke in a 5 series bmw (sorry!), then picked up, hesitated again...

It's better when warm, and when it does go it still goes like a bastard, but the idling is still all over the place. When does the secondary intake engage / disengage?

Sorry don't mean to hijack your thread stealthy!

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 12:08 pm

Stealthy, you haven't driven the car enough to get the trim values. They are all showing zero.

Air flow still looks OK.

Maybe it's a vacuum leak when the SAI is activated then. You might want to remove the N112 solenoid and test it. I have seen these fail letting air in through the body.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 12:13 pm

Or maybe one of the recombining valves is dead.

Image
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 12:15 pm

Check the condition of all of the little vacuum hoses while you are at it.

Shpongled, sounds like your air box isn't on properly. Who did the servicing?
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

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shpongled
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Re: severe misfire at idle

Post by shpongled » Sat Jul 07, 2012 12:49 pm

Thanks Shop, it was John Bowles down in Sevenoaks. Already went back there with it, but nobody there now to do any work on it today so logged the problem with them.

Is the air box something I can do myself? I'd like them to put it right ideally...

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 1:04 pm

Check the DIY spark plug thread for the air box.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

stealthyspeeder
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Re: severe misfire at idle

Post by stealthyspeeder » Sat Jul 07, 2012 1:05 pm

Thanks Shop! (I just went round the underground car park earlier!)

I will try and get those trim values populated this afternoon, I assume they are held within in the ECU when they appear? Im just thinking due to my laptop battery problem, I might have to drive around a bit first, then plug it in to the car. That will only work if those values are stored in the ECU and not in VCDS when a log is started.

I rang the parts store and asked him the model number of the plugs, they are NGK PFR7Q ones

Sorry for all the questions, you probably feel like you are dealing with a mouth breathing knuckledragger, but how does one test the N112 solenoid?

And the recombining valves?? I have never heard of them! (they're not Dump valves right?), I'll have to read up on them before I go finding and fiddling!

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Shoppinit
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Re: severe misfire at idle

Post by Shoppinit » Sat Jul 07, 2012 1:57 pm

Remove the N112 and the vacuum pipes on it. Suck the end that is in line with the axis of the valve. You shouldn't be able to suck any air through.

Activate the valve (either with 12V - the polarity is marked on the valve connector) and check that when you suck that air is sucked in through the perpendicular nozzle. Cover the nozzle up with your finger to make sure that it's not sucking air in anywhere else.

You can also activate the valve with the Vagcom. Go to output tests and go through them one by one until you get to the N112.

Follow the vacuum pipe from the perpendicular nozzle connection to the recombining valves. These are the round metal things at the back of the engine each side of the manifold. You can see one in the above photo: if the green N75 circle is a clock, it's at 8 o'clock.

You can suck on the pipe going to these valves. There should be a lot of resistance. If there isn't then the valves are knackered.

The pipe that goes onto the axial nozzle is the vacuum from the manifold and the vacuum reservoir. Follow this pipe until you get to a T piece. One side will go to the inlet manifold, the other side will go to the vacuum reservoir. You could try removing the T and blocking all the pipes up to see if your engine runs better. At the same time, block the pipes leading from the recombining valves.

This will throw codes for the SAI, but it might be useful for diagnosing.

Also, yes the ECU remembers the trim values.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

stealthyspeeder
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Posts: 82
Joined: Tue Jun 21, 2011 9:38 pm

Re: severe misfire at idle

Post by stealthyspeeder » Sun Jul 08, 2012 11:02 am

Thanks again Shop, I have left her in with a VAG specialist here in Dublin who is goin to look at it next week. The mental stress of my RS6 being sick day after day just got too much!

Hopefully he will be able to solve the issue and I will report back, I will send him a link to this thread if he has a look and is stumped! Thanks again!

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