Polo rough idle on cold start, idle stumble, etc

[flat6]

Did you end up finding the cause of this?

Starting to experience the same issue, when idling after driving at high speed the revs fluctuate between 680 - 750rpm, its a little uncomfortable with the new dogbone insert...

This was with shell 98, tried this morning with United 100 octane, it did help it feel a lot smoother but still noticing the rough idle randomly

Just had my car serviced recently to, mentioned it to them and they re-aligned the throttle body.

[s4mmie]

Unfortunately no

It's getting worse actually.. and I feel your pain about the dogbone insert exacerbating the problem.
I suspected an IC pipe leak, but I don't think that could be as I'm actually making more boost if anything.
Not sure if it could be caused by a faulty N75, but I suspect it's on it's way out as I seem to be making more boost than usual (2-3psi more) and boost has always been a little sporadic.. flat spot every now and then.

No idea at the moment, I've tried everything I can think of.. I've come to the conclusion I'll fix it when it breaks

[noone]

Polo rough idle on cold start, idle stumble, etc

I'd be interested to see a video of your tacho needle, I think mine is often moving around a little on idle, more noticeable before its warm.

[flat6]

I'll try grab some footage of it when it happens, unfortunately its quite random but generally happens on the way to work.

Hmm was thinking diverter valve may have been stuffed but noticed your running the forge with the same issue

[mitchr6]

Have only had my gti for a few weeks but have noticed that mine is rough at idle when cold and sluggish until i get about 1km down the road. When i rev it it is smooth but is just roughish at idle.

[VWindahouse]

After the new tunes my needle jumps a little at idle especially in traffic (no probes with the phase 2 tune - see below). I guess it's in correlation with the cooling system as the revs jump a little when the fan kicks in then drops low after causing a rougher idle than before.

So both times the new tunes were loaded I asked Gav to increase the idle to about 8-900 rpm and all is sweet!! (and I think that's what we did with the phase 2 tune also)

[s4mmie]

I'll try grab some footage of it when it happens, unfortunately its quite random

Ha, that was going to be my reply

Have only had my gti for a few weeks but have noticed that mine is rough at idle when cold and sluggish until i get about 1km down the road. When i rev it it is smooth but is just roughish at idle.

The first thing I'd be checking is the SAI pump. Mine had the exact same symptoms so I ditched it, all good now

After the new tunes my needle jumps a little at idle especially in traffic (no probes with the phase 2 tune - see below). I guess it's in correlation with the cooling system as the revs jump a little when the fan kicks in then drops low after causing a rougher idle than before.

That's interesting Ant, I'd never thought about the fans kicking in (prob cause I can't hear them ) but that actually sounds like what is happening with mine; Every so often, sitting there idling and it will stumble down to 500rpm and then shoot back up to normal. The odd timing of it would fit in with fans kicking in as well. I'll have to check it out...

Not sure about the constant fluctuations though, it seems to hunt from 700-750 all the time. I'm not worrying about it atm, got the timing belt coming up soon and still want to go CC (one day! ) so I'll hopefully sort it then.

[noone]

if you have a cable, you can use lemmiwinks to raise the idle a bit, see if its happier.
Have you changed your plugs recently?

[flat6]

After the new tunes my needle jumps a little at idle especially in traffic (no probes with the phase 2 tune - see below). I guess it's in correlation with the cooling system as the revs jump a little when the fan kicks in then drops low after causing a rougher idle than before.

After driving home this afternoon with the new tank of fuel I didn't notice the issue at all, but I think you may be spot on about the traffic scenario, every morning I deal with bull**** traffic, and I notice it most then, driving home its not so bad..

This afternoon it behaved, so its quite possibly the fans kicking in!

I have noticed it behaves differently when I revert back to the stock tune, I might try the APR 95 octane tune and see how it goes, it really doesn't like the shell 98 I get at my local servo on the 98 tune.

[flat6]

if you have a cable, you can use lemmiwinks to raise the idle a bit, see if its happier.
Have you changed your plugs recently?

Going to order a cable off ebay, any specific one people recommend?

[gavs]

After driving home this afternoon with the new tank of fuel I didn't notice the issue at all, but I think you may be spot on about the traffic scenario, every morning I deal with bull**** traffic, and I notice it most then, driving home its not so bad..

This afternoon it behaved, so its quite possibly the fans kicking in!

I have noticed it behaves differently when I revert back to the stock tune, I might try the APR 95 octane tune and see how it goes, it really doesn't like the shell 98 I get at my local servo on the 98 tune.

If the fans kicking in are making the idle stumble that much, I'd be looking at either your alternator or hopefully just your battery is on it's way out.

One thing that the 6R has for it's models is that on cold starts, it opens the throttle and dumps a lot more fuel into the system to get the oxygen sensors warmed up and operating properley as quickly as possible, resulting in loud,rough stummbling idle for the first 90 secs of operation and lumpy idle until the temps all hit around 60 degrees. Is this something that could be the same as the cold start issues some of you are mentioning? I'm not that familiar with the 9n engine's progression...

[VWindahouse]

It's after the fans stop Gav. The revs seem to drop lower than when the fans were off by 100 or so rpm creating a lumpy idle. Only seems to happen in cooler weather though.

[h100vw]

Going to order a cable off ebay, any specific one people recommend?

Any old cable should be ok for using lemmiwinks. Don't expect proper VCDS capability though.

Mitchr these are 9N GTI idle issues, not sure if you had noted that. The 6R is a different ECU type amongst other things.

Gavin

[flat6]

Can confirm the issue is caused by crap fuel using the APR 98octane Tune,

Filled up last week with United 100 octane, didn't experience any issues all week

Just filled up today with Shell 98, bam, rough idle, rougher to drive, however switched the tune to the APR 95 Octane and its ok, Got a feeling were not really getting 98 octane fuel.

Anyone else noticing this with Shell 98 at the moment?

Edit: after further testing, even on stock tune its still stuttering, bad batch for sure, dodgy bastards

[noone]

I try to only use BP98, seems to be the best for performance when I tried a few, read similar from others.

Would it be worth replacing the fuel filter now? Might be worth using a injector cleaner additive for peace of mind.