Wobbly idle

[GLM]

Hi chaps - i'm after a little advice...

The other day i was stuckin a traffic jam for about 15min with the car being up to temp but not over heating, i found that whilst sat there not moving the idle would fluctuate to the point where the car would be almost stalling. Although it didnt actually stall, due to the low idle the engine was knocking a fair amount to the point it was making the car wobble, but more worryingly, on the dash the gear selection indicator on the DIS would start to flicker between S and D until the idle was sorted back out by the electornics.

This happened twice whilst stuck in the jam. On the second occasion it was just as i was about to move along - at first there was little response and then as the idle/revs came back to normal i almost got launched into the back of the car ahead (not sure if it was me not paying attention and watching the needle with my foot on the gas or if it was the car over compensating for the revs initially being too low).

Anyone else had this sort of issue?

I was thinking it may be that the engine is a little bunged up with carbon and needs a good boot. I was also wondering if its worth using shot of those engine cleaners that go in with a tank of fuel - do they work??

The car has only done 27k, is stock and at the moment is being used for fairly short journeys.

Any suggestons or advise would be appreciated.

Thanks
luca

[doodlebug]

You need Vag Com.

Dealer time.

[RS6chris!]

<beep> batch of fuel?

[GLM]

Well the car is covered with monidal, so will see how it goes. Will also use it as a n excuse to give the car a good run this weekend and clear the pipes out and put in some v-power.

Cheers

[PorkaFly]

I don't think its Vag Com time...this is something mine has done every so often in exactly the situation you describe over the whole time I've had it since 2009. Not as severe as yours sounds, but recognise the scenario and the dip in revs, followed by wobble and then sorting itself out again. I've always put it down to being driven mostly in London...a good clearing of its throat (full throttle up-shifts) does the job. You will find a system check will find nothing/no error codes, maf etc. I was intrigued to watch Ed China (yes I'm a secret Wheeler Dealers fan) do a terra clean on an engine recently and the difference/result after decoking was impressive. I also read recently that running a few tanks with an additive in it also does a good job of degunking the fuel system. On the bad fuel point, I've never experienced this after an Asda fill-up...usually a Shell fill-up...and it has done it on regular and super so all things considered I don't think it is fuel, bad fuel or octane related.

Oh, and. Luca, mine is on 28k miles '09 plate...

PF

[classba]

I too think it's short journeys and coke up that courses this issue.

A blast on the open road should do it. I do however only use Shell Nitro+ every fill up and ohhhh, don't let the tank run too low otherwise, you will suck in all the crap on the bottom of the tank which could block injectors and fuel filters.

I do use a bottle of Wynns High Performance Petrol Fuel Additive once every 6 months or so just to keep the system clean. You can feel the difference after the tank of fuel with the additive.

[GLM]

thx PF and classba.

Yeah, i've have seen on Fifth Gear as well as Wheeler Dealers them use those additives and get quite surprising results, figure it may help. Still, a good thrash will come first i think!!

[rushey]

Mine tends to labour a bit on starting first thing in the morning, splutters into life over a smooth fire up. Fine once running although as I didn't take go for any warranty (due to re map) I am going to 'over service' so to speak so booked in next week. Only on 23k miles but I also do lots of short journeys so guess this isn't helping. Any others using additives ?

[adsgreen]

Can also be useful to reset the fuel trims.

Times I've had this with other cars is when the battery is playing up. the cold weather will show up any imperfections or signs of age in the battery.
also the other one is alternator as if the voltage is out of tolerance very very strange things can happen.

[rushey]

Would that be picked up on a service inspection - going to mention the slight miss when starting up from cold.

[adsgreen]

No chance unless it was really really low. Not sure if the ecu would throw an error if the voltage was out of spec.

[Ricky.REP]

If you are getting misfires from cold then check RMVB 32 and 33 in Vagcom.....

If the fuel trims are all over the place then you have a split vacuum house in the km's of them hidden in the engine bay!

Quite common cause on RS6 and RS4 running issues tbh!

Have to find and repair vacuum leaks on quite a few I work on!

[RS6chris!]

I've said it before....I'm convinced the heat this lump generates causes issues under the hood.

My oil seal leak
And my weepy rocker cover gaskets
And...brittle oil return breather pipe(snapped)

Even the master tech said oil seal and rocker gaskets were brittle/perished as if damaged by heat?

Just my ten pence worth!!!

[PorkaFly]

If you are getting misfires from cold then check RMVB 32 and 33 in VAGCOM.....

If the fuel trims are all over the place then you have a split vacuum house in the km's of them hidden in the engine bay!

Quite common cause on RS6 and RS4 running issues tbh!

Have to find and repair vacuum leaks on quite a few I work on!

Ricky - interesting info thanks. Wouldn't it do this all the time then rather than very rarely/occasionally if there was a vacuum leak?

Txs
PF

[Batfinnk]

I'm no expert but would say if the vacuum pipes do crack or split as with any material they will shrink when cold and expand and reopen the weak point when hot so could explain the inconsistent rough running which is then diagnosed as vacuum pipe issues.