Rising and falling rev counter needle on idle

[northern monkey]

Had my S3 for a few months now and since I bought the car the rev counter needle rises and falls by about 50rpm while idling.
I have had Audi look at it and they diagnosed the induction system needed cleaning. I had it cleaned and it seemed to make a little difference at first but now is the same as it was. There is a new air filter fitted aswell.
Without keep going back to Audi to charged a fortune to fix nothing. Is there anyone out there that can help diagnose what the issue might be?

Graeme

 

[bengal]

Try unplugging the maf and if it stops then its probably the maf at fault. Could also be a vac leak but try the maf first.

 

[northern monkey]

Sorry to be dim.
What is the MAF? I had thought about a vac leak but thought Audi would've checked for that first.

 

[bengal]

Between the airbox and intake pipe there is a plastic cylindrical part with an electrical plug thats the maf so you need to unplug it and run it unplugged to see if it cures it. As for audi imo some of them are not all there cracked up to be so its very possible for them to miss simple things like a vac leak the same applies for general garages as well you would be much better off with an audi specialist.

 

[bengal]

Or a good tuning garage.

 

[JD09]

Think this could also be temp sender related? From what Welly said, unless I've misunderstood, the temp sender or thermostat itself might be faulty...

 

[NoggyS3]

Think this could also be temp sender related? From what Welly said, unless I've misunderstood, the temp sender or thermostat itself might be faulty...

Really...?

 

[Alex C]

Think this could also be temp sender related? From what Welly said, unless I've misunderstood, the temp sender or thermostat itself might be faulty...

mmm, have you replied in the wrong thread?

 

[Welly]

I could have sworn I replied to this thread already - but apparently I didn't.... weird....

The symptoms you describe are the symptoms I would expect to see from a simple vac leak. Hunting at idle is normally a vac leak off the manifold, or a leak elsewhere in the charge system.

Don't expect Audi to be able to diagnose everything. IMO they are simply the same monkeys you get down your local garage in fancy uniforms, called 'technicians'.

Start with a good old vac leak hunt, check all the pipes off the lower side of the manifold. Personally, I'd buy some cheap silicone hose from ebay, in various sizes (3mm, 4mm and 5mm) and simply replace all that you can. At least this way you KNOW it's not a vac leak.

Also check for splits in the DV hose, and the pipes around the EVAP canister (the clicky thing that sits by the header tank).

As JD said, the CTS can have some odd effects on the cars when they go, BUT, it's normally related to starting the engine when it's warm, so I wouldn't suspect that here.

 

[JD09]

Really...?

mmm, have you replied in the wrong thread?

I thought it was the third thing to check, along the lines of this thread as well...

http://www.audi-sport.net/vb/a3-s3-forum-8l-chassis/107361-thermostat-temp-sender.html

Might be wrong though! Must have mis-read lol!

 

[Alex C]

 

[JD09]

Shush you, it's been a long day*







*Read year

 

[northern monkey]

Thanks guys.
So homework for tonight. I have work out:
1. What the CTS is and what it looks like?
2. What the EVAP canister is and what it looks like?
3. Which are the DV hoses?
I hope I don't sound ungreatful. I'm merely highlighting I know near to nothing.

G

 

[Madeley]

Had my S3 for a few months now and since I bought the car the rev counter needle rises and falls by about 50rpm while idling.
I have had Audi look at it and they diagnosed the induction system needed cleaning. I had it cleaned and it seemed to make a little difference at first but now is the same as it was. There is a new air filter fitted aswell.
Without keep going back to Audi to charged a fortune to fix nothing. Is there anyone out there that can help diagnose what the issue might be?


Graeme

Have you had the throttle body cleaned? a dirty one can cause these symptoms.

 

[finesse]

Shush you, it's been a long day*







*Read year

on asn I answer fits all

boost, vac leak turbo gone blaa blaa

 

[northern monkey]

Yip. I had the throttle body cleaned by Audi, Which hasn't changed a thing.
How difficult is it to change the said hoses? Does anyone have any recommendations on good quality, but not expensive hoses? Ideally not bright blue Samco ones.

Graeme

 

[Welly]

It's not hard, it just a case of replacing like for like.

Something like this (4mm BLACK SILICONE VACUUM HOSE TUBING SILICON PIPE TUBE on eBay (end time 03-Dec-10 12:04:46 GMT)) will be fine, I've used it in the past with no issues at all.

Like I said, get a few sizes to cover all bases. I'd go for the black myself.