Quick easy favor request if you have vagcom

[Hofahome]

I want to compare my values to another car to figure out my idle issue.

1. Please have car at normal op temp and at idle
2. Use vag com to look at engine speed, torque and throttle valve angle on both Engine and ABS modules. No need to log, just write down or take snapshot of the values
3. Many thanks and good car karma to someone who helps a brother out

[Loe]

Engine:
699/m
58.875Nm
3.282* -3.384*

ABS
672/min
51.0-56.1Nm
0.0%

[Hofahome]

Engine:
699/m
58.875Nm
3.282* -3.384*

ABS
672/min
51.0-56.1Nm
0.0%

Thanks man!

[whiped]

More data for you:

Engine:

Engine Speed - 700/min
Engine Torque - 38-42 Nm
Throttle Valve Angle - 2.867*-2.986*

ABS:

Engine Speed - 672/min
Engine Torque - 35.7 Nm
Throttle Valve Angle - 0.0%

Interesting to see my data compared to Loe's.

[Loe]

A/c off? Mine was a/c on.

[whiped]

Mine was on but the temp was set to 72, it was cooler than that outside so probably wasn't actually running.

I can do a proper log if you are curious.

[mrmomo313]

AC off
Engine:
680/min
37-38Nm
2.713*
Abs:
672/min
35.7Nm
0.0%





AC on-set to 65F
Engine:
680/min
54-55Nm
3.538*
Abs:
672/min
56.1Nm
0.0%

[Hofahome]

This issue is driving me bonkers. It happens even on stock flash btw, so not a tune issue. When the A/C is on, the problem is non-existent and I can't think of a reason why.

My idle speed and throttle valve angle seem to match up pretty well with you guys (at least when idling normally ~700rpm). When the idle slowly surges from 1.1k to about 1.8k rpm, the idle speed and throttle valve angle go up pretty well together.
The only difference seems to be with the A/C off, the torque sits around 20-24nm, however with the A/C on the torque matches up with you guys in mid 50nm.

[Hofahome]

I was looking more at the fault codes and noticed something very odd. Mind you the time and date stamps are different.


6262 - Idle Control System RPM
P0507 00 [237] - Higher than Expected.
MIL ON - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 7
Mileage: 79439 km
Date: 2016.09.24
Time: 17:57:24

Engine speed: 1014.00 /min
Normed load value: 1.6 %
Vehicle speed: 0 km/h
Coolant temperature: 96 ∞C
Intake air temperature: 50 ∞C
Ambient air pressure: 840 mbar
Voltage terminal 30: 14.116 V
Unlearning counter according OBD: 40
Engine speed: actual: 896 /min
MAF_ENVD: 70.81176 mg/stroke
Coolant temperature (unfiltered): 94.50 ∞C
Ignition angle: actual: 1.125 ∞
MAP_1_ENVD: 238.79883 hPa
TPS_ENVD: 1.6 %


16957 - Vehicle Speed Sensor
P0501 00 [096] - Implausible Signal
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 80067 km
Date: 2016.10.01
Time: 13:43:59

Engine speed: 1231.00 /min
Normed load value: 2.0 %
Vehicle speed: 0 km/h
Coolant temperature: 95 ∞C
Intake air temperature: 52 ∞C
Ambient air pressure: 850 mbar
Voltage terminal 30: 14.218 V
Unlearning counter according OBD: 39
Engine speed: actual: 1216 /min
MAF_ENVD: 70.81176 mg/stroke
Coolant temperature (unfiltered): 95.25 ∞C
Engine: operating status: PU
Battery voltage: 14.218750 V
Vehicle speed: actual: 0 km/h

Mind you I am not really sure what MAF_ENVD means or what to take from this. It is just too specific of a number on two different occasions to be coincidental. Any ideas?

[Loe]

MAF is the mass air flow that's "modeled" from using other sensor data. The ENVD means environmental data.

Essentially, the error occurred or triggered (or more accurate, was logged as an error) during that air mass value.

I would check the following:
-throttle sensor (worse case scenario)
-throttle connections
-vacuum leak
-intake leak

[Hofahome]

Ok I think I understand now. Correct me if I am wrong. Basically the ECM is thinking that at 70.8111mg/stroke, the rpm should be around 700rpm or at the very least not as high as what is being reported by the speed sensor (in this case the crankshaft position sensor, which reports the RPM.) It throws codes for the idle being too high and also one saying the RPM is likely not correct. In essence, the ECM thinks that the crankshaft sensor is lying to it. However, the crankshaft sensor is likely ok because my rpm gauge works fine and other things like misfires would be occurring. SO, this would lead one to believe that it is an issue with 1) ELECTRONIC INTERPRETATION OF AIRFLOW: either throttle sensor is under-reporting the % the throttle body is open, a short in the wiring between the throttle body and ECU, or faulty MAF - or in this case modeled MAF from our 3 sensors; 2) VACUUM LEAK - take your pick of causes (PVC, EGR, etc) 3) FUEL: faulty regulator or leaky injectors? or 4) an ECM that is basically a paranoid schizophrenic - misinterpreting the normal messages.

Sound about right?

- My bet is either the throttle sensor or the wiring at this point. (Of note, I was cruising the other day at about 70mph in 5th and give it half throttle, but nothing happened for a few secs, then it accelerated; also when sitting at a stoplight I can sometimes hold the throttle in the 1.2-1.4k range and let off - but the rpm will stay there)
- MAF/MAP sensor doesn't make much sense given that I have logged both post-compressor values, and they seem very close. It would be odd for both to fail. I have already replaced the pre-s/c sensor with no change as well.
- vacuum leak - still unsure but I would assume this would always affect the idle and especially when cold. However the idle is more unstable in heat. I kind of wonder about the secondary air system somehow letting unmetered air in.
- fuel system- after logging the pressure values, nothing seems bizarre. I have run fuel system cleaner (chevron formulated for e85 as well) several times and it did not seem to affect the issue at all
- bad ECM - possible. not sure how to rule this out though

Sorry to ramble, just putting some thoughts together. Let me know if you have any ideas or areas to look at via vag-com.

[Loe]

The symptoms you've describe could also swing in favor of a vacuum leak. I would look into that first (least expensive method) and then look look into the sensor. I wonder if we can compare values in VCDS (voltage)?

[jdwk]

Just ran into this same situation and codes. Made a few trips today without issue, but my idle started creeping up at a stop light to about 1500 rpms and then dropping back to 1k and repeating. This continued after I got home. I let it idle for a while and it eventually threw the codes, P0501 and P0507.
It continued this behavior until I shut it off and let it sit for 15 minutes. Idle was fine after that and for another two short 5 miles trips. It certainly seems like a vacuum leak, but not sure why it would come and go since it is unrelated to heat.
@hofahome, I know this was a long time ago, but do you recall what the cause of the problem was?

[jdwk]

CEL turned itself off on the next trip and hasn't come back on after a few more drives, idle has been perfect. Really wish I knew what caused this hiccup. In my experience, if you don't root cause a problem, it will inevitably come back, and usually at the worst possible time.