Abnormal MAF readings at idle? (and some engine vibration)

[WeekendDriver]

I've heard 3.37-3.47 g/s being quoted as typical MAF reading while idling at ~720 RPMs. So I've decided to check this value on my car, as a very rough but very simple MAF health test. And this is what I've got:



720 RPM, 18.8% engine load, 2.50 g/s mass flow. Which seems low.
Then I slightly pushed the gas pedal until I achieved steady RPMs slightly higher than idle:


920 RPMs, 15.0% engine load. RPMs went up, load went down, is that normal? And oddly enough, MAF again reads 2.5 g/s, although I have clearly seen it go up to ~3.5 g/s in the 880-980 RPM range. This particular value could be a glitch, I guess.

On top of that, my engine is vibrating at 720 RPM (its idle after warming up). The vibration is not severe, and repair shop mechanic told me it's normal (the shop specializes in VAG). Still, Idon't think it's normal. The vibration disappears at ~800 RPMs. It's clearly produced by the engine block itself. I've got brand new original engine mounts, all three of them.
As you can see, I was also monitoring misfires, and didn't see any.

So, what do you think about these MAF readings? And what's with the engine load figure? And could any of this be related to the vibration that's starting to get on my nerves after 3 years owning this car?

[old guy]

Download Unisettings and play around with the idle RPM and idle torque (channels 1 and 14). Make baby step adjustments and document the changes. You should be able to dial in a silky smooth idle by adjusting those values.

[WeekendDriver]

Download Unisettings and play around with the idle RPM and idle torque (channels 1 and 14). Make baby step adjustments and document the changes. You should be able to dial in a silky smooth idle by adjusting those values.

Thanks for the workaround. But wouldn't it be treating symptoms instead of treating the illness?

[mp3driver]

Clean it. Don’t spray it with anything. Just very gently Qtip the carbon off of it. Sounds stupid but my b5 did something similar. Showed me 220grams during a log and after qtip read 265 grams which fixed my lean issue. Just be very careful not to damage the sensor


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[old guy]

Thanks for the workaround. But wouldn't it be treating symptoms instead of treating the illness?

Not sure you have an illness. I have my idle set at 800 rpm. Depending upon prevailing conditions my MAF g/s ranges between 2.5 and 3.5 and engine load ranges between 16 and 22%. Just find your sweet spot for a smooth idle.

Edit: Prevailing conditions would be ambient temperature, A/C on or off, engine temperature, headlights on/off, etc. All can change the engine load and g/s as the ECM makes adjustments to maintain the correct idle rpm.

[Kevin C]

The vibration is probably the motor just hitting a resonant frequency. That's why a small change in rpm makes it go away.

[obaka]

My car had some vibrations at idle it was a vacum leak, it fixed the brakes too

[mp3driver]

My car had some vibrations at idle it was a vacum leak, it fixed the brakes too

If you have access to Ross tech you can check the fuel trims for a vacuum leak Condition.


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[WeekendDriver]

If you have access to Ross tech you can check the fuel trims for a vacuum leak Condition.

I have a significant negative value in the 033 measuring block, which, as I understand, is the opposite of a leak (engine running rich instead of lean). Taking out the oil probe results in significant positive values as expected.
Thanks for the advice. I suppose even if there is a problem that causes the engine to vibrate, there's no reason not to adjust idle RPMs to avoid this annoying condition.

[mp3driver]

I have a significant negative value in the 033 measuring block, which, as I understand, is the opposite of a leak (engine running rich instead of lean). Taking out the oil probe results in significant positive values as expected.
Thanks for the advice. I suppose even if there is a problem that causes the engine to vibrate, there's no reason not to adjust idle RPMs to avoid this annoying condition.

I would just verify there isn’t anything else being overlooked. Exhaust touching chassis, Motor mounts damaged? Once all the variables are exhausted then sure change your idle. The only time I’ve stumbled across the odd vibration is typically because of a high durometer motor mount was used and passes all of the shake into the car chassis from the engine when running. Good luck!


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[Gin+]

The vibration is probably the motor just hitting a resonant frequency. That's why a small change in rpm makes it go away.

x2

[WeekendDriver]

I would just verify there isn’t anything else being overlooked. Exhaust touching chassis, Motor mounts damaged?

Both engine mounts are new OEMs.
Where could exhaust be touching the chassis?

Also, it's not the car body that's vibrating, it's clearly the engine block itself (which doesn't tell us a whole lot, I guess).

[mp3driver]

When do you feel this. If the block itself vibrates and not the car then why is it bothering you?


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[mp3driver]

My exhaust is larger than stock and the fitment wasn’t perfect. So on occasion it rest against the rest sub frame area and causes a little vibration.


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[WeekendDriver]

When do you feel this. If the block itself vibrates and not the car then why is it bothering you?

Good point. Let me rephrase: I can see that the engine block is the source of the vibration. It does transfer onto the car body eventually, I can feel it on the steering wheel and sometimes even with my lower back (very slightly, but unmistakably).

[Natejo91]

Old Guy- If we have a Motoza tune (or any other tune for that matter) will Unisettings be able to write and/or change these parameters?
Some tuners lock down the ECU/ECM don't they?

[old guy]

Old Guy- If we have a Motoza tune (or any other tune for that matter) will Unisettings be able to write and/or change these parameters?
Some tuners lock down the ECU/ECM don't they?

I have used Unisettings with the GIAC big injector file on numerous occasions. I've also used it with my Motoza tune. Kinda fun to play with it: Clicky click®

[Natejo91]

I have used Unisettings with the GIAC big injector file on numerous occasions. I've also used it with my Motoza tune. Kinda fun to play with it: Clicky click

Thanks for the read! Quick question though, what cable do you use for the Unisettings? I tried using my Ross Tech Hex Net and it wouldn’t recognize it. Do I need to do something to set up the interface settings? I couldn’t find a user manual anywhere...

Anyhow, assuming OP has access to VCDS (based on the images posted) i just tried the idle speed adaptation on my car yesterday.

01 engine -> Adaptation 10 -> Channel 01 then change then enter a value from 124 to 132. My car was at 128 and I had a decent vibration coming thru the steering wheel and the seat for a while but just assumed I was hyper sensitive or something. So I figured I would give this a try. Started entering values starting at 124 and worked my way up. I think I settled on 126 and it isles soooooo much smoother.


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[WeekendDriver]

Anyhow, assuming OP has access to VCDS (based on the images posted) i just tried the idle speed adaptation on my car yesterday.

01 engine -> Adaptation 10 -> Channel 01 then change then enter a value from 124 to 132. My car was at 128 and I had a decent vibration coming thru the steering wheel and the seat for a while but just assumed I was hyper sensitive or something. So I figured I would give this a try. Started entering values starting at 124 and worked my way up. I think I settled on 126 and it isles soooooo much smoother.

Thanks for the tip and detailed info on how to do this!
Does lower value mean higher idle RPM?

[Natejo91]

To be honest I don’t know what the value corresponds to. I just changed the value to find what felt right. I really didn’t see much change in idle speed. I think when it was said and done my idle was around 820 rpm. But I can check again when I get home if you want.


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[old guy]

Thanks for the read! Quick question though, what cable do you use for the Unisettings? I tried using my Ross Tech Hex Net and it wouldn’t recognize it. Do I need to do something to set up the interface settings? I couldn’t find a user manual anywhere...

I use a generic cable and a FTDi chip driver to interface with Unisettings.

If the OP has a registered full version of VCDS he should be able to use that the same way you did and adjust his idle speed.

[WeekendDriver]

But I can check again when I get home if you want.

No need, thank you, I'll go ahead and see if I can access this functionality, and then I'll follow your steps. Was just curious if you decreased or increased the RPM to get the smooth idle.