Hrm.. engine idle oddness

Solari · 2 Jan 2009 at 17:16

I know there are a few knowledgable VAG people on here so was wondering if anyone can give me some pointers...

I've noticed that some days when idling, the rev counter needle is stable at about 800 RPM but about every 4 seconds, it'll dip down to about 600 then go straight back up again. It's ticking over OK and doesn't sound like it's about to conk out or anything. I haven't noticed anything else untoward.

Should I be concerned? The car is going in for service next week so I'd like to get this investigated and fixed at the same time.

Cheers chaps.

paradigm · 2 Jan 2009 at 17:32

What is turned on electric wise?

Mine had an irratic idle when the aircon was on and it was due a re-gas.

Or, tried a VAG-COM?

loltim · 2 Jan 2009 at 17:36

Vacuum leak maybe?

Beerbaron · 2 Jan 2009 at 17:38

my a3 does the same. it can idle above 1k and then randomly drop.

Scuzi · 2 Jan 2009 at 17:38

My Toledo 1.8T did this for the entire 3 years I owned it. It didn't seem to happen unless the engine was idling for a long time, i.e. 5 mins+ then it would kick in. It became more regular towards the end of ownership but I never really worried about it as I sold it for a song.

( |-| |2 ][ $ · 2 Jan 2009 at 17:38

From my experience this is going to be a dirty throttle body, faulty MAF, Coil pack or temp sensor. Wait until it gets worse then it i'll be easier to fault find.

Solari · 2 Jan 2009 at 17:41

paradigm said:
What is turned on electric wise?

Mine had an irratic idle when the aircon was on and it was due a re-gas.

Or, tried a VAG-COM?

Air-Con was regassed about 6 months ago

Also had a split breather pipe replaced at the same time.

Good point about what's on - I think I've had the heaters on but that's about it. I'll try tonight with them turned off. I don't have VAG-COM but the garage I use can do it when I put it in I guess.

I was more wondering if this is on the long list of common Mk4 faults and also hoping it's not a symptom of something more serious.

Re: above post, the coil pack has already been replaced. But good point, I will ask them to clean the throttle body while it's in for service. Shouldn't cost much. Thanks

[SKR]Phoenix · 2 Jan 2009 at 17:52

Solari said:
Air-Con was regassed about 6 months ago Also had a split breather pipe replaced at the same time.

Good point about what's on - I think I've had the heaters on but that's about it. I'll try tonight with them turned off. I don't have VAG-COM but the garage I use can do it when I put it in I guess.

I was more wondering if this is on the long list of common Mk4 faults and also hoping it's not a symptom of something more serious.

Re: above post, the coil pack has already been replaced. But good point, I will ask them to clean the throttle body while it's in for service. Shouldn't cost much. Thanks

the coil pack? you got 4 dude!

oh and I'd keep a spare in the boot, along with a spare DV.

Solari · 2 Jan 2009 at 17:55

[SKR]Phoenix;13198702 said:
the coil pack? you got 4 dude!

The whole lot was replaced (sorry, assumed the "pack" meant all of them) as per the VW recall recommendations some time ago

Surely if one had gone then it'd run "lumpy"?

[SKR]Phoenix · 2 Jan 2009 at 18:05

Solari said:
The whole lot was replaced (sorry, assumed the "pack" meant all of them) as per the VW recall recommendations some time ago Surely if one had gone then it'd run "lumpy"?

How old are they? They don't last forever, so you could have another failure. If one fails totally, then yes it should be lumpy as hell. However, I have found that they don't suddenly go and I can feel the car getting more and more lumpy over a few days/weeks. VAG Com will ident a prob though.

Solari · 2 Jan 2009 at 18:08

[SKR]Phoenix;13198811 said:
How old are they? They don't last forever, so you could have another failure. If one fails totally, then yes it should be lumpy as hell. However, I have found that they don't suddenly go and I can feel the car getting more and more lumpy over a few days/weeks. VAG Com will ident a prob though.

They were swapped about a year and a half ago IIRC. Maybe a little longer. Thanks for the advice

ethos · 2 Jan 2009 at 18:33

Try cleaning your throttle body (gasket is about £1.30) and then resetting with vag-com?

Air leak?

Age of spark plugs / coil packs.

If you have vag-com you can do a run and log any misfires on each cylinder. Might be useful...