# MK4 VRT Lean (MAF?)



## Korfu (Feb 26, 2007)

Symptoms - idles rough with miss fires - cel for running lean - unplug MAF immediately idle smooths out and runs great. With MAF unplugged it stays right around 14.7 A/F with about 15 vacuum. Car when driving at part throttle at times with switch between lean then rich then lean. At one check it was adding 20% fuel for its trimming (with MAF still plugged in).

With MAF unplugged car runs perfect, almost dead on A/F mixes under load, idle, and part throttle - no misfires. 

Im puling my hair out here tyring to figure this out, I put a new MAF in ran good for a bit then it started doing this again, cleaned it put in an air straightener cleared the codes and again rain good for a bit. I just ordered a AEM dry filter to replace the K&N oiled filter thinking maybe it that is causing the issue?

Specs on car:
6262 PTE turbo
PTE 39mm Wastegate
TiAL 50mm QV - re-circulation 
C2 Intake manifold
4" MAF
630 Injectors
9:1 compression (head spacer)
UM Stage 3 tune
Genesis Mk4 High-Flow Intank Fuel Pump
262 CAMs
MK3 Fuel Rail with 3 Bar

Is my head in the right place thinking that it has to be MAF related? If so why am I eating MAFs? Wiring is all good on it.

P4C


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## masterqaz (Oct 5, 2007)

Changing to a dry filter may help, is the sensor getting oily? That filter looks like its been restricting flow slightly as the plys are twisting although that maybe from handling.

Make sure you dont have any leaks upstream from the maf. It looks to be a good distance from the turbo so thats good as well.

Guessing Um 630 tune doesnt call for a promaf of some sort?


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## Korfu (Feb 26, 2007)

Made a makeshift leak detector and got it to 30PSI didnt find any leaks. No the UM tune does require a ProMaf just a 4" inlet, although the thought of getting one had crossed my mind if i keep burning through these OEM mafs. If there was a leak wouldnt I see it reflected on my wideband with the maf unplugged as well?

As far as if the maf is getting oily its hard to say it doesnt really feel too oily but then again I dont touch it in fear of hitting the sensor, but it does seem to respond well to CRC Maf cleaner so its possible.


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## masterqaz (Oct 5, 2007)

If its responding well to cleanings Id suspect that to be your issue. How long can you drive it after a cleaning till it begins to respond poorly?

Id pull the filter and clean it out or go for a ride on a damp day when the dust is down without the filter on.


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## R32Smoker (Oct 21, 2010)

My car also seems to run better with the maf unplugged. When running with the maf unplugged does it just read directly from the front o2 sensor? Is it safe to run it this way on low boost briefly?


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## Korfu (Feb 26, 2007)

masterqaz said:


> If its responding well to cleanings Id suspect that to be your issue. How long can you drive it after a cleaning till it begins to respond poorly?
> .


I last time I got to 60 miles. Time before that it was closer to 120miles. Driving from Baltimore to Ocean City it was good at part throttle no codes etc. Once I got into OC and traffic it started to act up again and go so bad I couldnt drive it anymore. A/F would go from 10 to sweep to 17+ then back to 10 then back to 17+. Parked it and ignored it for a day or two - removed maf and drove it home with no maf hooked up.


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## masterqaz (Oct 5, 2007)

R32Smoker said:


> My car also seems to run better with the maf unplugged. When running with the maf unplugged does it just read directly from the front o2 sensor? Is it safe to run it this way on low boost briefly?


Without the maf it'll use tps rpm to base load calculations


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## tim00 jti (Feb 1, 2008)

What tune do you have?

UM & C2 use a 4" MAF, Unitronic uses a 3.5" housing. If that's wrong, the cross sectional area of the MAF is off by 1.57sqin, and your car will be confused as all hell. That's what I believe is wrong with my car, I'll let you know after this weekend what happens when I switch from a 4" to a 3.5".


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## Korfu (Feb 26, 2007)

I def have the right size maf housing. I got a known good MAF sensor from a friend but am still waiting on the new filter to arrive, I wish places around me sold 4" inlet filters but alas they do not. If I dont have the filter by Monday I wont be able to mess with it again till mid November due to work traveling. 

Getting closer to just putting it away for the winter at this point.


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## Korfu (Feb 26, 2007)

Any way to test the O2 sensor to see if it lazy? I know via vagcom they don't read that quick to begin with.


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## GinsterMan98 (May 19, 2008)

Korfu said:


> Any way to test the O2 sensor to see if it lazy? I know via vagcom they don't read that quick to begin with.


Narrowbands are all lazy. Your best bet is to swap the filter or get a Pro MAF. I bet it would run like a raped ape with the Pro Maf. You can however use Vag-com to check you short and long term fuel trims. They should be +or- 3% from zero. Once they get over 18 is when you will get a code. This is happening because the misfire will fool the ECU that its running rich so it will pull fuel and then run lean. The cycle will continue until it trips a code. Solve the misfire issue first, which may be something simple like MAF air turbulence or inlet/filter setup. Pro Maf > OEM MAF. I was starting to burn through them at higher boost levels. I know others on here have had tons of MAF failures on chip tuned Vr's.


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## V-dubbulyuh (Nov 13, 2005)

GinsterMan98 said:


> Narrowbands are all lazy. Your best bet is to swap the filter or get a Pro MAF. I bet it would run like a raped ape with the Pro Maf.


He is a 12v Mk4... ie no Pro-Maf (this product never made it to see the light).


And agree with Ginster 100% here, MAF problems on Mk4 & 630 combinations are very common. I clean mine frequently or the software performance drops off in a huge way. As said before, get a dry filter, given how tempermental that setup is you want to eliminate any other issues such as oil etc coming into contact with that MAF element.


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## Korfu (Feb 26, 2007)

Thanks guys - the new filter got held up due to Sandy but showed up today. The car battery is completely dead so it will prob be the weekend before I get time to mess with it again.


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## gti vr6er (Oct 8, 2010)

Stay tuned take a Mk4 Pro MAF option. I started the thread regarding having problems with the UM 630 file. My guy says he talked to Jeff and he's swapping a mk4 harness into his mk3 to work out some problems mk4 guys are having with the 630 file(rich at idle, bogging, missing under load, etc). He said he might be working on a pro maf option for mk4's which leads me to believe his tune doesn't like our maf's so I'm almost certain your problem has something to do with your maf/tune.


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## gti vr6er (Oct 8, 2010)

Stay tuned take a Mk4 Pro MAF option. I started the thread regarding having problems with the UM 630 file. My guy says he talked to Jeff and he's swapping a mk4 harness into his mk3 to work out some problems mk4 guys are having with the 630 file(rich at idle, bogging, missing under load, etc). He said he might be working on a pro maf option for mk4's which leads me to believe his tune doesn't like our maf's so I'm almost certain your problem has something to do with your maf/tune.


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## V-dubbulyuh (Nov 13, 2005)

gti vr6er said:


> He said he might be working on a pro maf option for mk4's .


That was to come out a while ago, then the stock Maf was determined to be adequate and not enough customer interest to warrant development on the Pro-MAf... if/when it is released due to more interest from the 12V Mk4 crowd I am all over it because the Mk3 Pro-Maf was a huge improvement over stock. :thumbup:


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## GinsterMan98 (May 19, 2008)

V-dubbulyuh said:


> That was to come out a while ago, then the stock Maf was determined to be adequate and not enough customer interest to warrant development on the Pro-MAf... if/when it is released due to more interest from the 12V Mk4 crowd I am all over it because the Mk3 Pro-Maf was a huge improvement over stock. :thumbup:


My bad on that, thought they had it for MK4 cars.:beer:


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## Korfu (Feb 26, 2007)

Ok All here is where I am at. Put the new maf in (it was used) car hated it. Cleaned the maf that I had just bought off put it back in with the new filter and it made no real difference. Unplugged the maf car still ran the same. So I no longer think its the maf? We read the Wideband and it was fluctuating between 1 and .984 and never anything else, no where near what the wide band gauge was showing. Unplugged the wideband and it stayed the same fluctuation. Plug it back in and bingo it started showing real close to what the gauge was showing. Started to idle better and all. Went for a quick drive and the A/F was all over the place, super rich then super lean. Miss fire on sudden acceleration and begged at 10 (rich) on the gauge during good load. Part throttle seemed fine for the most part. Here is the log from vagcom

Also I noticed that the vacuum I am getting at idle is about 11-12 on the gauge (AEM TruBoost) this seems low from what I have read from others, sounds like it should be closer to 18-20? Or is it due to my cams and compression?


```
Saturday,03,November,2012,15:00:19:19544,VCDS Version: Release 11.11.4,Data version: 20120807
021 906 018 S,, United 630 08     V08 ,

,Group A:,'031,,,,Group B:,'032,,,,Group C:,'002
,,Lambda Control,Lambda Control,Bin. Bits,Bin. Bits,,Adaptation (Idle),Adaptation (Partial),Bin. Bits,Bin. Bits,,Engine Speed,Engine Load,Injection Timing,Mass Air Flow
,TIME,Bank 1 (actual),Bank 1 (specified),,,TIME,Bank 1 Sensor 1,Bank 1 Sensor 1,,,TIME,(G28),,,(G70)
Marker,STAMP,,,,,STAMP, %, %,,,STAMP, /min, %, ms, g/s
,0.22,0.961,0.984,        ,        ,0.53,0.0,0.0,        ,        ,0.82,800,21.8,2.05,2.67
Saturday,03,November,2012,15:01:03:19544,VCDS Version: Release 11.11.4,Data version: 20120807
021 906 018 S,, United 630 08     V08 ,

,Group A:,'031,,,,Group B:,'032,,,,Group C:,'002
,,Lambda Control,Lambda Control,Bin. Bits,Bin. Bits,,Adaptation (Idle),Adaptation (Partial),Bin. Bits,Bin. Bits,,Engine Speed,Engine Load,Injection Timing,Mass Air Flow
,TIME,Bank 1 (actual),Bank 1 (specified),,,TIME,Bank 1 Sensor 1,Bank 1 Sensor 1,,,TIME,(G28),,,(G70)
Marker,STAMP,,,,,STAMP, %, %,,,STAMP, /min, %, ms, g/s
,0.60,0.914,0.984,        ,        ,0.01,0.0,0.0,        ,        ,0.30,760,21.8,2.05,2.61
,1.50,0.891,1.016,        ,        ,0.90,0.0,0.0,        ,        ,1.20,1160,32.3,4.10,13.58
,2.40,1.172,0.984,        ,        ,1.80,0.0,0.0,        ,        ,2.10,760,18.0,2.46,8.75
,3.30,0.766,0.992,        ,        ,2.70,0.0,0.0,        ,        ,3.01,1240,35.3,4.10,8.17
,4.21,1.203,0.961,        ,        ,3.61,0.0,0.0,        ,        ,3.90,1920,23.3,2.46,13.47
,5.11,1.023,0.992,        ,        ,4.51,0.0,0.0,        ,        ,4.81,2720,22.6,2.87,17.42
,6.01,1.062,1.016,        ,        ,5.41,0.0,0.0,        ,        ,5.71,3480,20.3,2.46,22.61
,6.91,1.008,1.016,        ,        ,6.31,0.0,0.0,        ,        ,6.61,3240,3.8,1.23,3.78
,7.81,1.452,0.930,        ,        ,7.21,0.0,0.0,        ,        ,7.51,2280,13.5,1.64,11.39
,8.70,0.750,0.852,        ,        ,8.10,0.0,0.0,        ,        ,8.41,2520,39.1,5.33,23.00
,9.60,0.883,0.906,        ,        ,9.00,0.0,0.0,        ,        ,9.30,2920,39.1,4.10,24.72
,10.50,1.039,0.992,        ,        ,9.90,0.0,0.0,        ,        ,10.20,3320,33.1,3.28,26.83
,11.40,0.984,1.016,        ,        ,10.80,0.0,0.0,        ,        ,11.09,2800,6.0,1.23,8.67
,12.30,1.086,0.969,        ,        ,11.70,0.0,0.0,        ,        ,12.00,2440,21.1,2.87,16.75
,13.20,0.750,0.828,        ,        ,12.60,0.0,0.0,        ,        ,12.90,2600,27.1,4.10,22.58
,14.10,0.750,0.813,        ,        ,13.50,0.0,0.0,        ,        ,13.80,2840,55.6,6.97,30.56
,15.00,1.000,1.016,        ,        ,14.40,0.0,0.0,        ,        ,14.70,3120,39.1,3.69,25.58
,15.90,0.969,1.016,        ,        ,15.30,0.0,0.0,        ,        ,15.60,2560,6.8,1.23,7.58
,16.80,0.750,0.828,        ,        ,16.20,0.0,0.0,        ,        ,16.50,2200,49.6,7.79,20.81
,17.70,0.750,0.821,        ,        ,17.10,0.0,0.0,        ,        ,17.40,2320,52.6,6.15,23.14
,18.60,0.750,1.016,        ,        ,18.00,0.0,0.0,        ,        ,18.30,2440,53.4,5.33,23.03
,19.49,1.016,1.016,        ,        ,18.90,0.0,0.0,        ,        ,19.20,2440,8.3,1.23,7.06
,20.39,1.991,1.047,        ,        ,19.79,0.0,0.0,        ,        ,20.09,2360,4.5,0.00,3.64
,21.29,1.991,1.047,        ,        ,20.69,0.0,0.0,        ,        ,20.99,2280,4.5,0.00,3.39
,22.19,1.991,1.047,        ,        ,21.59,0.0,0.0,        ,        ,21.89,2120,4.5,0.00,3.42
,23.09,1.991,1.047,        ,        ,22.49,0.0,0.0,        ,        ,22.79,1960,4.5,0.00,3.19
,23.99,1.991,1.047,        ,        ,23.39,0.0,0.0,        ,        ,23.69,1840,4.5,0.00,2.86
,24.89,1.991,1.047,        ,        ,24.29,0.0,0.0,        ,        ,24.59,1720,4.5,0.00,2.50
,25.79,1.991,1.047,        ,        ,25.19,0.0,0.0,        ,        ,25.49,1600,4.5,0.00,2.28
,26.68,1.991,1.047,        ,        ,26.09,0.0,0.0,        ,        ,26.38,1480,3.8,0.00,2.14
,27.59,1.413,0.969,        ,        ,26.98,0.0,0.0,        ,        ,27.28,840,15.0,2.05,5.08
,28.49,0.899,0.969,        ,        ,27.88,0.0,0.0,        ,        ,28.19,1880,11.3,1.64,8.25
,29.39,0.750,0.969,        ,        ,28.78,0.0,0.0,        ,        ,29.09,1920,28.6,2.87,5.50
,30.29,0.945,1.016,        ,        ,29.68,0.0,0.0,        ,        ,29.99,1880,20.3,2.05,9.50
,31.19,1.640,1.016,        ,        ,30.59,0.0,0.0,        ,        ,30.89,2880,14.3,2.05,19.22
,32.09,0.750,0.828,        ,        ,31.49,0.0,0.0,        ,        ,31.79,3120,29.3,4.10,30.50
,33.00,0.867,0.805,        ,        ,32.40,0.0,0.0,        ,        ,32.70,3720,54.1,6.97,52.42
,33.97,0.961,0.805,        ,        ,33.30,0.0,0.0,        ,        ,33.63,4760,54.1,8.20,91.42
,34.97,0.938,0.992,        ,        ,34.31,0.0,0.0,        ,        ,34.66,4840,6.8,1.23,11.39
,35.86,1.991,1.047,        ,        ,35.27,0.0,0.0,        ,        ,35.56,2560,4.5,0.00,3.03
,36.76,1.991,1.047,        ,        ,36.17,0.0,0.0,        ,        ,36.47,2200,4.5,0.00,3.22
,37.66,1.991,1.047,        ,        ,37.06,0.0,0.0,        ,        ,37.36,2040,4.5,0.00,3.11
,38.56,1.991,1.047,        ,        ,37.96,0.0,0.0,        ,        ,38.26,2000,4.5,0.00,3.06
,43.06,1.991,1.047,        ,        ,43.36,0.0,0.0,        ,        ,42.76,1800,4.5,0.00,2.56
,43.96,1.991,1.047,        ,        ,44.26,0.0,0.0,        ,        ,43.66,1760,4.5,0.00,2.64
,44.86,1.991,1.047,        ,        ,45.16,0.0,0.0,        ,        ,44.56,1720,4.5,0.00,2.42
```


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## Korfu (Feb 26, 2007)

Plugs are gapped at .028


Im starting to think its a boost/vacuum leak again but we didnt find any with the home made tester. I really wish I had access to a smoke tester.


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## TBT-Syncro (Apr 28, 2001)

Korfu said:


> Also I noticed that the vacuum I am getting at idle is about 11-12 on the gauge (AEM TruBoost) this seems low from what I have read from others, sounds like it should be closer to 18-20? Or is it due to my cams and compression?


you'll never see proper vac numbers when its not stoich.


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## Korfu (Feb 26, 2007)

Just went for a quick 'drive' Apologies for the qualit I was attempting to drive, shift, and record at once.


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## TBT-Syncro (Apr 28, 2001)

i dont trust your wideband.

if its working properly, its either bad maf, or BAD vac leaks. whats your maf reading at idle once warmed up? whats the coolant reading once warmed up? 02 trim at idle once warmed up?


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## spitfire481 (Mar 21, 2007)

coolant temp sensor was reading at low 90s maf at idle was high 2s low 3s the wide and was real close to what the vag com was reading

OP using vortex superstar account


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## Korfu (Feb 26, 2007)

spitfire481 said:


> coolant temp sensor was reading at low 90s maf at idle was high 2s low 3s the wide and was real close to what the vag com was reading
> 
> OP using vortex superstar account


In addition if I had that big of an vacuum leak wouldnt I expect to see the car stall?


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## TBT-Syncro (Apr 28, 2001)

Korfu said:


> In addition if I had that big of an vacuum leak wouldnt I expect to see the car stall?


no. not normally. 

what was the 02 trim at idle?


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## Korfu (Feb 26, 2007)

I was using Joes vagcom and laptop to pull that info. I will see if I can borrow it Mon/Tues and pull that info because I cant remember with a good level of certainty

PS we are going to do another leak test this next weekend when we have some more time, if the leak test doesnt reveal an issue I might get one more new MAF and see if it helps but this would be the third maf in less than 1500 miles and at $200 a pop its getting a bit ridiculous, but I did get the new non oil filter so it might of been that.


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## R32Smoker (Oct 21, 2010)

It seems the Mk4 UM 630 tune has some issues, your not the only one with problems with this tune.


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## TBT-Syncro (Apr 28, 2001)

R32Smoker said:


> It seems the Mk4 UM 630 tune has some issues, your not the only one with problems with this tune.


the issues that are shown in this video have nothing to do with a tune having 'issues'. 

there is clearly a significant sensor or hardware issue.


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## tim00 jti (Feb 1, 2008)

Any updates? I'm still having issues with my car, I'm about to pull trigger on standalone with new harness. Screw OEM gremlins.


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## Korfu (Feb 26, 2007)

I havent really had anytime to work on it. Hopefully I will get some time in a week or two.


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## Korfu (Feb 26, 2007)

Switched to the 42# file and it runs great now. No other changes. Jeff said he will reflash the 630 once he has time to adjust the tune a bit more. 

Thanks to Jeff from UM for working through this with me.


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## R32Smoker (Oct 21, 2010)

Glad to hear you we're able to getting running well man, I think I'll have to pick up some 440s and do the same than. Happy New Years :beer:


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## Korfu (Feb 26, 2007)

Thanks, We only took it for one 30 minute or so drive with a several 3rd gear pulls. The first couple it ran pretty lean but after that the ECU must have trimmed out WOT because it was running pretty much dead on 12-12.9 a/f on WOT. Cruising I had no bucking and part throttle was great. It was dailyable again in my opinion (not that im going to daily it).

When going to park I stalled it (so used the my mk6 jetta clutch) and the battery is so dead it couldnt even roll the windows down so we just pushed it back into the parking spot until I can get a new battery and fix a coolant leak.


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## V-dubbulyuh (Nov 13, 2005)

^ But you will be returning to the 630 once Jeff has time to improve it correct?


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## Korfu (Feb 26, 2007)

Thats the plan, but since I am not going to track the car its a toss up whether I need 425hp or 475hp. I still plan on adding water meth regardless.


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## V-dubbulyuh (Nov 13, 2005)

PM'd


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