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both myself and many other RS4 owners seem to have developed problems with the idle speed/missfire after being serviced. just had my "new" RS4 serviced by Prestons and low and behold this ones started skipping a beat at idle, nothing serious but it is starting to get on my tits.

An Audi tech came out on Friday and luckily it was the same guy who came out to my last missfire. He spent a lot of time checking as much as he could, but he gave me this usefull nugett of info from his days at porsche roadside.

It turns out Porsche had a similar problem with the 996t, whereby after it had a service at an offical porsche centre, engine would missfire shortly afterwards or the engine would "destroy" itself. The problem turned out to be that after the oil was changed and the engine was restarted, the engine running without whilst the oil got round the engine caused irreparable damage even though it was only for a few seconds.

Has anyone got any further thoughts info on this?

Jon,

Sorry to hear your having problems with this one too.
Some VW guys have mentioned this skipping a beat too.
My Corrado VR6 does it too once in a while but I simply put it down to the fuel as it gives no fault codes, there is no loss of compression on any cylinder, and runs fine in every other respect.

Did they change the plugs ??
I found that putting platinum plugs in the VR made things a lot better.

I could be wrong here but I thought the 996t was a dry-sump engine, so even if the filters are changed and the oil tank emptied, it still retains good oil pressure on startup (assuming the oil filters have been pre-soaked !).
btw from posts made on www.rennlist.com I think I'm correct in saying the n/a 996 is no longer drysumped, which is why so many of them suffer problems when tracked on a regular basis (same goes for the boxster too).

Hope you get it sorted mate.

The only reason can be that the engine needs too much time to fill the new oil filter. Unless it is filled, the oil pressure is low. Prefilling should help, but no mechanic will do this if you don't watch him.

I find the lack of oil thing difficult to believe, when you drain the oil there is always a coating left on the moving parts, even if you don't use the magnetic oil [img]images/graemlins/smirk.gif[/img] and it shouldn't take long for an oil pump to get to pressure otherwise this would be a problem every time you left it overnight.

however maybe after they use an engine oil flush or a rebuild there would be problems.

Hmmm got me thinking though, I like changing my oil regularily, but if it causes more wear after a change then maybe it's best not to change it at all [img]images/graemlins/confused.gif[/img]

their picking it up on thursady and taking it to Preston Audi to give it a once over. Suprisingly Audi have been extremely helpfull.....they must have been on the happy pills again.

i will post the results....hope it's fixed for the cannonball!

I find the oil explanation a bit hard to believe. If lack of oil caused wear then the symptoms would worse than a simple misfire on idle. Maybe it's new plugs or just a bad tank of fuel?

BTW, after I change my oil I do NOT run the engine immediately. I fire it up and turn it off almost immediately a couple or three times. This ensures that the oil has circulated before it starts to run properly. Of course I'm not going to pretend that I KNOW this is necessary, just that I think it's a good idea.

I fail to see how starting it two or three times is any better than leting it run. It takes the same amount of work to lift the oil round the engine in both cases, so what is the difference ? I have built several engines from scratch, and I am a qualified engineer so I do know what I am talking about (;))

BTW, on my Mk1 Golfs and Beetles (originals) I used to remove the relevant ancillaries and run the oil pump with an electric drill to build pressure. I also fill the oil filter before screwing it on if possible. That is one of the largest holes that requires filling with oil in the event of a change.

'cos it does it at much lower revs?

Like I said, I just thought it was a good idea.

P.S. I've built engines from scratch too, and I'm also a Chartered Engineer, but as I'm sure most people here will agree, I haven't got a clue what I'm talking about! [img]images/graemlins/062802beat_prv.gif[/img]

wow, so many chartered engineers and experienced engine builders!! I'm impressed!
Can we have some consense here so that those non-technical folks that just love driving great audis can derive some tangible recommendations going forward.

I believe in you, guys
d. [img]images/graemlins/kissmyrings.gif[/img]

Jon, did you fit a cat back system??

I'm a Chartered engineer but in software engineering, does that help ? [img]images/graemlins/grin.gif[/img]


I too have built several engines, and would not recommend the 'starting several times' approach.

Being scientific about this, the oil pump will deliver the same amount of oil per rev, regardless of the rpm (What will differ is the engine stress and wear rate).
Note that oil pressure increases with revs, and should therefore be turned over at least at tickover speed.


It is generally accepted in tuning books I've read that the engine should be cranked with no plugs fitted until oil pressure is present (most sports cats have oil pressure gauges) as this means the pressure can be built up without the engine having any of the stresses of actually running.

If you've got carbs you can do this with them dry, so there is no chance of washing the bores with petrol.
If you have fuel injection then having no plugs should ensure that a fair percentage of the fuel is expelled anyway - so don't look down the plug holes while cranking !

As for the cats, well, not sure on this one, but I would work on the principle that you shouldn't be cranking it for very long, so the amount of fuel that could find its way to the cats shouldn't be very much.

I'm no expert on this. Just knowledge gleaned from several sources including bike and car engine builders, mechanics, club racers, tuning books, etc.
Sounds to me like there are differing opinions, and chances are the damage done from something like this is not likely to be significant unless you run your engine to its limit all the time (i.e. racing, sprints, rallying, etc)

Just my opinion [img]images/graemlins/thumbs.gif[/img]

Cheers,
John.

hkg - nah this car is completely standard

everyone else, i'm just as confused as anybody....including Audi! I'm just trying to gather opinions and possible answers to help them fix this anpying problem

Hmmm must be an engineers car I am chartered as well though electrical, and have rebuilt some engines, I go with the plugs out option after a rebuild and turn it over on the starter motor to pressurise, don't bother with that after an oil change as in my opinion modern oil pumps are so efficient these days, so I just let it tickover.

As John says, plugs out and fuel disconnected is the ideal way. And if possible, just spin up the oil pump without cranking the engine.

Thanks for the advice guys - I'll just fire up the engine as normal next time.

Anyway - did we get a conclusion to the original problem: I still find it hard to believe that an idling problem is caused by an oil change!