Hi all, coming back to you with a puzzle hoping I can benefit from your knowledge as seasoned owners.

 

My car is a 1Z 56 reg BWA ENGINE 2.0L TFSI.

 

I have an intermittent issue which is driving me (and my mechanic) nuts. Sometimes, when the engine is properly warmed up, say after 20-30 min of driving my idle speed fluctuates before it settles to around 750RPM. This happens when I put the car in neutral (i.e. approaching a traffic light, junction, moving in slow traffic). On 1 out of say 5 occasions it will shut the engine as it goes below 500rpm, especially when moving in slow traffic slightly uphill (this seems to make is worse). Just discovered tonight that once the issue occurs it does it even when parked up if I rev it to 2500-3000rpm and then let go. Youtube video link to follow shortly..

No EML, no faults recorded by the ECU which makes it more difficult.

 

A bit of background on the car itself for context:

Bought as spares or repairs with 82k on the clock, replaced with a 28k miles engine and gearbox off a donor car.

It had a new Forge DV + blowoff which failed within a week (read mechanical fail on tester but no split, just actuator fault) so put the original one back in but left the blowoff aliminium part in. I also found that the intercooler hose was loose at the time so tightened it up. Put new NGK iridium spark plugs in 

When the engine was replaced it had a new original timing kit put in, all new filters (original manufacturer fuel, oil, air, etc), high pressure fuel pump cover, gearbox oil, Millers engine oil, PCV deleted.

I also suspect that the car had a stage 1 remap as on live readings (engine running) torque was 399NM and turbo boost was 1.28BAR, alongside the fact that it does not seem to have a rev limiter.

 

Any suggestions are more than welcome guys before I sink my following wages into this without solving the issue. Promise I'll send a crate of beer over to whoever pinpoints the fault! 😁

Perhaps a vacuum leak somewhere on the intake side.

1 hour ago, MicMac said:

Perhaps a vacuum leak somewhere on the intake side.

Wouldn't this cause a constant fault though as opposed to an intermittent one?

Perhaps the leak is exacerbated by temperature.

 

I'm only having a go for the free beer!

7 minutes ago, MicMac said:

Perhaps the leak is exacerbated by temperature.

 

I'm only having a go for the free beer!

Might be the case as my mechanic said it might be related to vacuum, ignition (R8 coil pack going in on my next visit) air/fuel mixture (as a result of the remap), carbon build up on accelerator flap or intake manifold (even though it's unlikely on a 28k miles engine).

Already replaced MAF (which was off the original engine) with the donor engine's MAF after careful inspection to be on the safe side despite no signs of oil on it, etc.

 

When the DV issue happened the tester did come up with "air/fuel mix too lean" type of error (have a printscreen with all errors noted at the time which is lost in my 367477484 pics). 

 

What is weird is that there are no faults recorded, even though you would think that sensors are battling to get the idle speed settled as it goes up and down a couple if times before it stabilises around 750rpm.

 

@Tch1e any suggestions or "go to" gurus on this one by any chance? Willing to duplicate that beer crate order for pointing me in the right direction! 😂😋

Have you inspected the brake servo vacuum hose?  Not sure of the arrangement on your engine, but usually there's at least one stiff plastic pipe section and they tend to crack and leak at connections over hose barbs like the one-way valve.

2 hours ago, AlexTud said:

Hi all, coming back to you with a puzzle hoping I can benefit from your knowledge as seasoned owners.

 

My car is a 1Z 56 reg BWA ENGINE 2.0L TFSI.

 

I have an intermittent issue which is driving me (and my mechanic) nuts. Sometimes, when the engine is properly warmed up, say after 20-30 min of driving my idle speed fluctuates before it settles to around 750RPM. This happens when I put the car in neutral (i.e. approaching a traffic light, junction, moving in slow traffic). On 1 out of say 5 occasions it will shut the engine as it goes below 500rpm, especially when moving in slow traffic slightly uphill (this seems to make is worse). Just discovered tonight that once the issue occurs it does it even when parked up if I rev it to 2500-3000rpm and then let go. Youtube video link to follow shortly..

No EML, no faults recorded by the ECU which makes it more difficult.

 

A bit of background on the car itself for context:

Bought as spares or repairs with 82k on the clock, replaced with a 28k miles engine and gearbox off a donor car.

It had a new Forge DV + blowoff which failed within a week (read mechanical fail on tester but no split, just actuator fault) so put the original one back in but left the blowoff aliminium part in. I also found that the intercooler hose was loose at the time so tightened it up. Put new NGK iridium spark plugs in 

When the engine was replaced it had a new original timing kit put in, all new filters (original manufacturer fuel, oil, air, etc), high pressure fuel pump cover, gearbox oil, Millers engine oil, PCV deleted.

I also suspect that the car had a stage 1 remap as on live readings (engine running) torque was 399NM and turbo boost was 1.28BAR, alongside the fact that it does not seem to have a rev limiter.

 

Any suggestions are more than welcome guys before I sink my following wages into this without solving the issue. Promise I'll send a crate of beer over to whoever pinpoints the fault! 😁

https://youtu.be/wtgippnFE6c

Youtube link as mentioned before portraing the issue live.

4 minutes ago, Wino said:

Have you inspected the brake servo vacuum hose?  Not sure of the arrangement on your engine, but usually there's at least one stiff plastic pipe section and they tend to crack and leak at connections over hose barbs like the one-way valve.

Haven't done that, so will give it a try on my next visit and make sure everything looks fine. Saying that though, with it being likely caused by exposure to prolonged heat, it might not even be visible. Would this be likely to cause this behaviour as it probably makes sense with the lack of faults being recorded?

 

Access may be an issue for eyeballing or feeling, but usually a fingertip will pick up even small cracks that you can't get a line of sight to. 

Often seems to occur on downward facing side.  Can be far from small and very easy to detect by feel:

 

27 minutes ago, Wino said:

Access may be an issue for eyeballing or feeling, but usually a fingertip will pick up even small cracks that you can't get a line of sight to. 

Often seems to occur on downward facing side.  Can be far from small and very easy to detect by feel:

 

Wow! Quite a split in that pic and would defo feel it on fingertips. Also have an inspection camera available as a back up so you really got my attention now! 😁 Absolutely worth looking into! Hopefully my mechanic can look into it on Sunday when I'll be detailing his own car (which is one of my skills) as he's putting it up for sale. 

Will defo come back with an outcome and hopefully a beer order! 😁

@Tech1e 

 any suggestions or "go to" gurus on this one by any chance? Willing to duplicate that beer crate order for pointing me in the right direction! 😂😋

 

reposted this bit as I misspelled your username 🤪

 

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Evening guys,

 

Had to postpone the work on the car for quite a while but I finally managed to get it in the shop and get it sorted, so I thought I'd share the solution here.

 

The cause was the blow off valve, which has been removed. It caused the DV to malfunction somehow by taking air back in. As the MAP sensor had a different reading the electronics were wobbling the air/fuel mix causing the idle speed issue. 

 

The mechanic realised it as he timed the clicking sound of the DV opening/closing with the issue (variation in idle speed).

 

Prior to that we've refitted the PCV (new revised part+new seal) with the issue still occuring after. When he disconnected the MAP the issue disappeared but he kept looking for the cause as the MAP had been replaced previously.

 

A bit of work but at least not very expensive. One piece of advice - opt for the top rated aftermarket manufacturers for tuning parts.

 

One thing to clear - the DV that failed a few days after fitting was not Forge, but the latest VAG revision of it.

 

Thank you guys for getting involved and offering suggestions.

 

 

So who gets the beer? ;-)

On 21/02/2021 at 05:12, MicMac said:

So who gets the beer? ;-)

Sorry for dropping off the face of the earth for a while guys. 😋 Life's been nuts lately.

 

@MicMac I suppose you had the nearest suggestion looking at the replies. PM me your details and we'll get it sorted - I always keep my word.

Thank you all for getting involved and trying to help, I really appreciate it. 😉