1.6 BGU Idling problems when warm - diagnostic help?

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[solved] G'day all

I'm having a perplexing problem with my 1.6 MkV.
*Fuel consumption raises from 0.6-0.7 l/hr to 1.2-1.4 l/hr
*Idle surges, can occasionally stall
*Surging can be felt up to about 2000 RPM regardless of load
*Occasional reduction/loss of brake boost

But only if started when already warm, or driven for a fair while. VCDS codes are attached. I can't seem to upload the full scan as .txt



The car drives perfect for 20-30min, up to 2 hours if freeway driving. Symptoms appear after this.
*Symptoms appear immediately if car is restarted once warm, even if only driven for 10-15 min.
*Driving for approx 10 min after symptoms start sets ASR button, stability control dash light.


Fault codes don't appear to be set until after the ASR and stability lights come on. I checked codes today after warming up, but before restarting. No fault codes, but got the problems as soon as I restarted the car. I checked again, no codes. Codes were there when I got home 20 min later.


Things I've checked:
EGR Valve (electronic) - had minimal carbon buildup. cleaned it anyway, no change. Also ran the adaptation and got ADP OK. No visible damage to cables.
MAP/Intake Temp sensor - checked connector, in good condition. No buildup on sensor heads. No visible damage to cables.
Visual check of grounds - no apparent issues.


Has anyone experienced this before? Any suggestions what to try next?

Thanks

Causes:
Problem was caused by a temperature related EGR malfunction. The valve stuck in the open position when hot, but tested normal when cool.
Additionally the oil dipstick tube was not properly seated to the engine, and the crankcase breather tube was missing it's upper clamp. These alone would also have caused the same problems, excluding the high IAT.

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Recurrent Fault Codes - occur every drive after restart


17811 - EGR System - Regulation Deviation - Intermittent
Most Common| rare
Load1 83.5% | Load1 83.5%
Load2 3.1% | Load2 3.9%


16496 - Intake Air Temp. Sensor (G42) - Signal too Low - Intermittent
Most Common | rare
Temp 126.0c | 129.0c


ABS Brakes: (all instances)
01314 - Engine Control Module
013 - Check DTC Memory - Intermittent


Fault codes found more than once:
16784 EGR Malfunction Intermittent
Load 83.5%
Load 0%


16520 Lambda Sensor B1S2 Malfunction in Circuit - intermittent
RPM 1376
M.Air/rev 81.8
BIN 00100000
V 0.300V


RPM 1120
M.Air/rev 76.3
BIN 00100000
V 0.920V

[Umai Naa!!]

Check that the crank case breather isn't broken.

Likewise for fittings on the intake pipe.

[ball]

Thanks Umai. Had a closer look at the crankcase breather and noticed the top connection is kinda loose. It's sealed but seems like it can blow itself off under pressure. I'll try a test drive with it taped up and see how I go.

Edit: no change in behaviour unfortunately.

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Found the (mechanic replaced) dipstick tube was not fully seated, causing the PCV related symptoms.

I'm still getting shudder and poor fuel economy that I tracked down to a Cylinder 3 misfire. This only showed in Measuring Blocks, no code for some reason. From what I've read this would lead to unburnt fuel and throw the Lambda B1S2 error.

Insulation on the spark leads looks good and injector resistance is all good. Getting a socket tomorrow to pull and check the plug.

[Umai Naa!!]

Don't rule out the leads themselves.

They are easily damaged when the spark plugs are changed.

[ball]

The spark plugs I got out were just really old. Gap was 1.5-1.6mm instead of the specified 0.9-1.0. Replaced and had a quick run - no misfire counts. I'll find out if its truly fixed next time I have a longer drive.

Spark leads are in top nick. I'd have to check the service history but I'd bet on them having been renewed in the last 50000.

Spark plug changes on the BGU are tricky but doable without removing the manifolds. Tools needed: spark socket, double-u-joint connector and 1/2 drive extension bar. Plus some pliers to fish out dropped sockets

[ball]

Still no luck on this car. The misfire is gone for good but the rough idle, stalling, ASR and loss of brake boost still persist. I'm getting really tired of it.

My thoughts on what next are
- getting a vac leak test done ~ maybe that'll find breaks my visual inspection and aerosol sprays didn't
- theres something electric wrong ~ no idea what to do there

I also recently read about the Variable Intake Manifold valve. If it sticks in the wrong position that could contribute to idling issues while running fine under load. I can't work out if it's applicable from the little I've been able to find.

[Umai Naa!!]

Check the plastic vacuum pipe that comes out of the brake booster. Check every join, junction and fitting that connects to it.

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I'm having trouble getting at the brake vac line. It runs along the very top of the firewall hidden by the overhang so I can't see most of it.

Any idea what fasteners hold it on/where they are? I've had no luck finding guides or anything in the service manual.

Edit: 4 C shaped fasteners. First one faces down-left, remainder facing down. No damage found so far. Inline check valve is working.

[ball]

Brake vacuum line is near perfect. No splits or cracks anywhere, even at the fittings.