# Car runs better with MAF unplugged....WTF!



## norcalsurfer (Apr 6, 2011)

so i've been having a few issues with my '01 1.8t gti. i have the P0172 - System Too Rich, Bank 1 code. i replaced all the vacuum lines i thought were faulty, and changed out the MAF. 

i thought the MAF was bad prior to replacing it since when i unplugged it the car ran perfect. well i replaced the MAF and the car still runs like crap: stuttering a little bit while accelerating, not idyling well.

when i unplug the MAF the p0172 code goes away and the code for the MAF appears. not sure what this is about.

any help would be awesome!

thanks!


----------



## Vegeta Gti (Feb 13, 2003)

bad MAF perhaps
try get some maf cleaner..clean it..let it sit for an hour to dry..cplug in, clear codes and try again


----------



## norcalsurfer (Apr 6, 2011)

This is a brand new MAF from ECS Tuning.


----------



## Vegeta Gti (Feb 13, 2003)

did u get the good and the bad mixed up perhaps?

vacuum leak would be a lean code.

set the adaption for your O2's see if they test out ok


----------



## norcalsurfer (Apr 6, 2011)

No I didn't get them mixed up but I will double check.

How do I test the 02s?


----------



## schwartzmagic (Apr 29, 2007)

norcalsurfer said:


> No I didn't get them mixed up but I will double check.
> 
> How do I test the 02s?


This may sound kinda dumb but did you clear the code(s) after you swapped in the new MAF? I've seen sometimes where you replace a messed up part with a new one and the car won't run right immediately until you clear the old fault code(s). 

From what I remember if the O2 is bad a fault code will come up if you scan it using vag-com or an obd2 scanner.


----------



## schwartzmagic (Apr 29, 2007)

schwartzmagic said:


> From what I remember if the O2 is bad a fault code will come up if you scan it using vag-com or an obd2 scanner.


If its anything like adapting the throttle body then try this....

To test the adaptation for the O2s you have to use vag-com, select the engine module, select the measuring blocks, then the group # for the O2, then [Go!] then, [switch to basic settings]. That should work. Don't ask me about which group is for the O2 because I don't remember. You'll have to research that on your own. Visit the ross tech site or ross tech wiki.


----------



## forcefedjetta (Aug 14, 2003)

you may need to do a hard reset too disconect the battery and touch pos and neg together for about 10 min


----------



## lookin4avw (Apr 28, 2004)

Don't mean to hijack this thread, but since this came up I figured I'd ask. Regarding the hard reset, what's the difference between just disconnecting the negative terminal of the battery and disconnecting negative and positive connections and touching them together?


----------



## forcefedjetta (Aug 14, 2003)

touching them together dis charges all capacitors in the ecm so adaption is completely cleared


----------



## norcalsurfer (Apr 6, 2011)

Thanks I'm going to try the battery reset. Is there a specific procedure to this? I've heard of turning the key a click or two before touching the terminals together. Does this matter?


----------



## builtvw (Sep 20, 2009)

bump for the same-ish problem


----------



## builtvw (Sep 20, 2009)

bank 1... i assume thats bank1 sensor1...which would be your upstream o2


----------



## Cryser (Sep 9, 2009)

are you sure you got the right MAF, do the part numbers match?

to do an 02 sensor test you have to into 0bd2 functions on the main VCDS screen and select mode 5 02 sensors, there should be a testing option there.

while your car is idling, watch block 032 the voltage in the first window should switch from high to low within a second, if it's lagging your 02 sensor is on the way out. An 02 sensor test via the method above SHOULD detect this but not always.


----------



## norcalsurfer (Apr 6, 2011)

Well I did the hard reset to clea the adaptive and the code came back after an hour of driving. The first half hour the car feels great, then it begins to decline.

I don't have a vag-com to test the 02 sensors. Can I use a voltage meter?

I will double check the part numbers on the MAF.

Thanks for all the help!


----------



## Cryser (Sep 9, 2009)

you can use a voltage meter to monitor the 02, it's not the same as the vagcom test but you will get a general idea of their health... if you have a DSOM thats better so you can see the waveform


----------



## norcalsurfer (Apr 6, 2011)

NO LUCK........The part number is correct on the new MAF. I also changed out the upstream 02 sensor, new plugs, air filter, and fuel filter. Still am getting the same code.

I've about had it and am not sure what else to check. Any more ideas???


----------



## norcalsurfer (Apr 6, 2011)

Bump


----------



## norcalsurfer (Apr 6, 2011)

Any ideas?


----------



## Matt 337 (Apr 10, 2009)

What MAF did you get from ECS? I bought one and my fuel trims wouldn't adapted then after changing a bunch of other crap I put my old MAF in and my fuel trims adapted.


----------



## 87vr6 (Jan 17, 2002)

*FV-QR*

Did you by chance install it backwards... it DOES make a difference.


----------



## dubinsincuwereindiapers (Jan 16, 2008)

Probably not the maf....

Im dissapointed at id=27 lately. Especially you Chris Lolz

Its running better because its running in OPEN LOOP.. Probably a vac/boost leak, bad primary o2, etc, etc...

Cmon guys..

Id expect that response im the "emkay" forum.. Not here.


----------



## Vegeta Gti (Feb 13, 2003)

hey i took a glance and posted an idea man!! 

 been off the ball lately


----------



## dubinsincuwereindiapers (Jan 16, 2008)

Vegeta Gti said:


> hey i took a glance and posted an idea man!!
> 
> been off the ball lately


K.. Free hall pass breh..


----------



## Vegeta Gti (Feb 13, 2003)

:thumbup::beer::beer::beer::beer:


----------



## norcalsurfer (Apr 6, 2011)

Actually I bought the MAF from MJM. It's a reconditioned Bosch, part numbers match up. 

Maybe I missed a vacuum line that needed replaced??? Should I just replace them all even though they look ok and aren't visibly cracked? Car had 160k on it. 

It's idling crazy now, like on a cycle -- normal idle, then the rpms will drop for a second then the engine will give a burst and the rpms will spike and go back to normal after a second -- it keeps doing this at idle.


----------



## norcalsurfer (Apr 6, 2011)

Bump


----------



## norcalsurfer (Apr 6, 2011)

Sheizer!!!!! I'm getting the p0171 system too lean code now too along with the p0172 system too rich. Wtf??


----------



## Trackrocket (Nov 15, 2010)

Pre-cat O2 sensor...replacing mine on Monday, when it comes in from ECS.


----------



## norcalsurfer (Apr 6, 2011)

Not it, just replaced my pre cat 02 sensor. Still the same codes.


----------



## a81sturmer (Jan 3, 2011)

If it runs good at any time, like with the MAF disconnected, then my theory is it's probably not a vacuum leak. (I have the same problem/symptons on my 2000 1.8T Beetle that I have been troubleshooting off and on for the last 6 months. I have some posts on it.) But I'm no pro.

Hayes says with ignition on you should get 12V between the #2 contact on the MAF connector (disconnected from the MAF) and ground. On my car I see 8 volts gronded to the head and 10.5 grounded to the neg term on the battery. You might want to check that. Apparently it is common to have MAF connector/wiring harness problems. The #2 contact on the maf is the 2nd one (1st may be empty) from the curved side of the connector. Turn the connector so you see the contacts, and it should be clear.

I had to go buy a MAF, but I probably will. VW dealer wants $250. I'm really leaning towards new OEM Bosch from a parts house if I can find it. But like you, I'm afraid that's not the real problem...

Sure sounds like we are fighting similar problems. I dropped the $'s and bought the VAG COM, but until I have a couple full days to play with it, it's too complicated for my pea brain. It has been little help (my fault). Hell it took me a weekend & another $100 to get the Bentley manual accessible through the XP immulator in Win 7 Pro (NOT Win 7 Home).

I plan to work on mine the next couple days. Maybe we can help each other.


----------



## a81sturmer (Jan 3, 2011)

make that "I hate to go buy a MAF...", rather than "I had to go...".


----------



## dubinsincuwereindiapers (Jan 16, 2008)

I hate having to quote myself...


dubinsincuwereindiapers said:


> Probably not the maf....
> 
> Im dissapointed at id=27 lately. Especially you Chris Lolz
> 
> ...


----------



## norcalsurfer (Apr 6, 2011)

So now I'm getting p0172 AND p0171 --- too rich and too lean. How the F does this work?


----------



## a81sturmer (Jan 3, 2011)

Changed my mind about running good with MAF disconnected indicating no vacuum leak. Even if it runs good with the maf disconnected, there could still be a leak between the maf and the turbo. 

Running good with maf disconnected does mean the cat isn't plugged, and it means there are no bad leaks between the turbo and the intake, and the coil packs are probably good.

But THERE STILL COULD BE A LEAK BETWEEN THE MAF AND THE TURBO. To check for that I pressurized the intake system. It held 5 or 10 psi until it blew the clamped off PCV pipe to the diverter valve. I should have replaced it with a clamped off piece of regular hose first. The PCV pipe is too weak for the pressure.

Also, using vag com I determined that MAF wasn't flowing when hooked up. It had to be the maf or a leaks. No leaks so I replaced the MAF. Fixed my problem. Now I just need to replace the interior and suspension and A/C - Hah, hah (that means LOL). Insert colon, dash, close paren here.

Cheers folks.


----------



## dubinsincuwereindiapers (Jan 16, 2008)

For future reference...

Unplugging the MAF throws the ecu into "open loop"..

When in "open loop" the ecu ignores many sensors, and runs off of a 'safe' base map.

Hence during "open loop" operation the engine runs better when there is a problem somewhere.

It DOES NOT always mean that the MAF is bad.. In fact most times the issue lies elsewhere...


----------



## norcalsurfer (Apr 6, 2011)

Bump...any advice before I take 'er in?


----------



## dubinsincuwereindiapers (Jan 16, 2008)

Pull codes


----------



## norcalsurfer (Apr 6, 2011)

P0171 and p0172: too rich and too lean. Any ideAs?


----------



## TheBossQ (Aug 15, 2009)

norcalsurfer said:


> P0171 and p0172: too rich and too lean. Any ideAs?


At this point, you need to ignore the codes. Look at it like this, it's air/fuel/spark. As big a problem as you described having in closed loop, if it were fuel or spark, those problems would most likely show up in open loop as well. Therefore your problem is 99% air. You have a bunch of sensors replaced (IAT was the only thing I didn't see), so it's unlikely to be those.

I would test fuel pressure first, as it's the easiest next thing to do (even if it's less likely to be the problem). From there, you need to test for vacuum and intake tract leaks. Next would be wiring for the related sensors. Unless you have access to an oscilloscope, then the first thing I would do is black box test the related sensors.


----------



## jtturbo01 (Aug 2, 2009)

Im having the same problem..168k miles and mine has starting idling bad enough to cut off..just got it back from a mechanic today..he said his scanner checked out OK leading him to believe it is the throttle body assembly. I have checked and he checked and couldnt find any vac leaks anywhere, not to say we didnt miss one. It has a new MAF and new coils/plugs. Not sure if it really is the trottle body, i sure hope not.


----------



## Audis4noob (Nov 2, 2015)

Did anyone figure this out. I'm having same problem and have replaced maf sensor twice

Sent from my SAMSUNG-SM-G900A using Tapatalk


----------



## Alexiankoo (Jul 28, 2018)

Hey guys i am experiencing the same behavior on a 2018 Passat 2.0

Dealership mechanics are useless and every time i go back a service manager goes on a test drive around the block and tells me that its normal

I even asked what would happen in their opinion if the MAF gets disconnected from a working car and they told me the car would run better which is absolutely ridiculous answer

I had the car for 1 year and i have 31k miles on it and after 7 dealership visits my issue is still not solved/properly identified 


Sent from my iPhone using Tapatalk


----------



## Vegeta Gti (Feb 13, 2003)

Alexiankoo said:


> Hey guys i am experiencing the same behavior on a 2018 Passat 2.0
> 
> Dealership mechanics are useless and every time i go back a service manager goes on a test drive around the block and tells me that its normal
> 
> ...


completely wrong forum man. wrong engine, wrong platform,etc. you shouldn't have a MAF either. You car is under warranty and you're calling them out yet it appears you have very little mechanical knowledge yourself. If you're frustrated, take it to a local independent shop by searching your local regional forums or by posting in the appropriate platform/engine forum. you're about 13 years newer than any car here, at minimum.:beer:


----------



## Alexiankoo (Jul 28, 2018)

Vegeta Gti said:


> completely wrong forum man. wrong engine, wrong platform,etc. you shouldn't have a MAF either. You car is under warranty and you're calling them out yet it appears you have very little mechanical knowledge yourself. If you're frustrated, take it to a local independent shop by searching your local regional forums or by posting in the appropriate platform/engine forum. you're about 13 years newer than any car here, at minimum.:beer:


How can i dare post an issue about an internal combustion engine from the same manufacturer and 200 cc’s off 


Sent from my iPhone using Tapatalk


----------



## Vegeta Gti (Feb 13, 2003)

Because it's completely different management completely different injection type completely different maf type completely different platform.......

Sent from my SM-N950U using Tapatalk


----------

