# Please please please help with pesky P0172 code (Mk3 2.0 OBDII)



## Kiyokix (Dec 16, 2005)

Car: 1998 Jetta 2.0 5spd
Relevant Mods: C2 chip, techtonics 2.25 catback, 42DD Test pipe, Neuspeed P-flo

Code: P0172 that won't seem to go away, and I'm nearing the end of my thought process to fix it
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Okay so the car will do the normal daily driving thing just fine, it returns roughly 26-30mpg with my driving style, it will accelerate 'fine' but it's most DEFINITELY not full power, it doesn't stall, it will hold idle fine at roughly 1100 rpm or so (remember it's chipped). I can hear the car pop on shifts at times so I know it's running rich, as well as see the black tip on the exhaust.

The car made good power up until a few weeks ago, however NO parts were changed to coincide with the sudden power loss. So far parts that have already been replaced are as follows...

MAF
O2 Sensor (front as the rear is deleted with chip)
Coolant temp sensor
Air filter
Fuel pump
Fuel pressure regulator
Fuel injectors
Fuel rail
Fuel filter
Various vacuum lines
Fuel pump relay
Spark plugs
Ignition wires
Oil pressure switch (x2)
Catalytic convertor (replaced with 42DD pipe since it was partially clogged and I was strapped for cash)
Exhaust (replaced for the same reason)
Upper intake manifold gasket
Throttle body gasket
PCV (brand new factory)
PCV hoses
Valve cover gasket
Thermostat (old one was bad)
Ignition switch
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I BELIEVE that's everything relevant I've replaced on the car so far. Of course not all of that was changed to chase a problem (I'm not stupid lol), but all of those things could indeed be relevant to fixing the problem at hand.

*More details*

First time code appeared 
Short term fuel trim: -4.9%
Long term fuel trim: -0.7%

After replacing O2 sensor/coolant sensor (light appeared again maybe 1 month ago if that)
Short term fuel trim: -6.3%
Long term fuel trim: -3.41%

After replacing fuel pump/air filter (cleared code yesterday and it came back today after 103.9miles)
Short term fuel trim: -4.9%
Long term fuel trim: -7.5%

When you accelerate, sometimes the car will 'hiccup' slightly, when you let off the throttle sometimes the car will 'hiccup' (not sure what word to use) slightly. Normally if the hiccup off throttle happens, it will happen again as soon as you touch the throttle again. The car will still accelerate, it doesn't stall when it happens, but it will still happen.

When using my fuel pressure gauge for some reason it WILL read pressure when attatched to the fuel in-side of the rail, however it WILL NOT register any pressure when attatched to the fuel out-side of the rail. (it had already lost full power before I put the other rail on so I know that didn't cause it)

Looking at the plugs that were replaced showed me that the problem is on all four cylinders not any specific one. (all four plugs are nearly identical black rich look)

There is _no_ smoke coming from the exhaust (or anywhere else) on startup, running, high rpm, etc.

The MAF and throttle body have both been thoroughly removed and cleaned with the appropriate cleaners.

First start of the day (usually morningish) the car will accelerate smoother/harder in the first minute or so, but I still don't feel as though it's full power (which I have felt before).

The revs will hang when you put it in neutral when coming from speed sometimes, but not all the time. They don't hang up super high, only a little above idle (say 1600rpm), and only for a short while.

The car had the same idle before on the stock chip (swapped it out to make sure), so it's not the chip causing a problem.

When you first start the car the revs zing up to roughly 1800rpm or so, then they hold there for a quick few seconds before coming back down to idle most times.


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Okay so that's all I can think of at this time, HOWEVER if you want to see/hear video/audio of the car to help diagnose it I'm more than willing to do so. (my phone has super awesome video capability)

If you guys need anything further please don't hesitate to ask, and I'll do whatever I can to get this figured out. I want this engine light off finally, and I REALLY want full power back again badly!

Kei


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## stoveyy (Aug 18, 2007)

Have you checked into an evap leak? If its constantly purging evap fumes you'll get a rich code. Pull the purge off and see if you can blow through it


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## Kiyokix (Dec 16, 2005)

stoveyy said:


> Have you checked into an evap leak? If its constantly purging evap fumes you'll get a rich code. Pull the purge off and see if you can blow through it


Thanks, I went under the hood tonight after doing some research yesterday about just that. If the evap is what I think it is, then I grabbed a braided line and I could feel it 'pulsing' in my fingers continuously.

I made sure that it was not just vibration from anything else (it wasn't), but this felt like a VERY distinct pulsing through the line.

*OH! ANOTHER THING I FORGOT TO MENTION*

Whenever I'm fueling up the car, no matter what the temp is outside, no matter how low the system is...there is NEVER a hiss sound like I'm used to hearing when removing the cap from a fuel tank. There are no fuel leaks, and as I said ealier all of the fuel system components have been changed before (including the fuel cap and fuel pump ring). There is NO smell of fuel vapors anywhere in the car either.


Here is a picture I just now took of the line I'm talking about. It's located just behind the headlight on the passenger side under the intake area. Is that the evap you're talking about...can it be cleaned/fixed without having to get a new one?



Kei


(sorry, while I've been working on cars for a long time, I've never really dealt with emissions equip much)


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## PBWB (Sep 12, 2004)

First off, big props to you for giving EVERY possible detail concerning your car. It's people like you why I still log in to this crotch rot of a forum. 

Out of curiosity, can you throw up a pic of this TB spacer you have? Who makes it?

Also, do you by chance have your TB de-ramped? The throttle hang scenarios you describe are prevalent of de-ramping obd2 TB's. Either that or I suspect there might be something with the TPS going on here....

I would also suspect there's something wtih the EVAP going on. If you have a vag, can you check your readiness codes and tell us what the statuses are for each.


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## Kiyokix (Dec 16, 2005)

PBWB said:


> Out of curiosity, can you throw up a pic of this TB spacer you have? Who makes it?
> 
> Also, do you by chance have your TB de-ramped? The throttle hang scenarios you describe are prevalent of de-ramping obd2 TB's. Either that or I suspect there might be something with the TPS going on here....


First off thank YOU for sticking it out on this forum with me...I've thought more than one time about leaving with some of the nonsense that goes on here.

As for the TB spacer...I don't have one lol. I went back and checked to see if I mentioned something that like, and couldn't find it. My throttle body is also not deramped because I too have heard of too many issues that may arise from that.

EVAP wise though I believe we're onto something. I went out last night after taking that picture, and I tapped on the purge valve under the intake a few good times with my hand. I don't know if it was just a coincidence or not, but I started the car afterward and the 'pulsing line' wasn't pulsing quite so hard this time so I drove it around for a few minutes.

The car didn't have a hiccup moment for a long while, and felt again like it had full power...almost tempting me into a ticket lol. (officer was near the end of my road while I was checking acceleration up to around 40mph in a 35zone)

I think I'm going to go outside and remove that valve if I can get some new hose (and clamps) to put on, to give it a check inside. I don't know if it can be cleaned or not, but looking around the internet it seems other cars mention cleaning it on their forums so maybe?

Of course that could've just been a coincidence, so we'll see.

Kei


(as for vagcom, I've got software but no cable yet lol)


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## PBWB (Sep 12, 2004)

Yea, my bad. I saw you had replaced your TB gasket and somehow thought you had mentioned a spacer. :banghead:



I'm going to look into mine purge solenoid now too.....Luckily I've been through enough cars that I have spares of everything. Right now I have the evap line removed from the TB and plugged. I did this because after de-ramping my TB I kept throwing a 0172 code for being rich, so in the midst of trying something random, removing that line from the TB made the CEL go away.  But that's a different story.

And if you get new hose make sure it's rated for fuel.


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## stoveyy (Aug 18, 2007)

Easiest way to check a purge valve definitively is too use a hand vacuum pump. It should hold vacuum one way and not hold vacuum the other. And it should hold vacuum on the one side for a while. I.e lose a few inches if that in 5+ minutes. 

Just cause it clicks doesn't mean it's good. And if you need a purge valve. Search my name. I just made a thread on how to buy them cheap.


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## stoveyy (Aug 18, 2007)

I'm rather confident in condemning your purge valve though. A leaking purge valve will allow gas vapor that shouldn't be there to be there all the time. You'll get rich conditions and you will also get a hanging idle. Or surging idle.


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## Kiyokix (Dec 16, 2005)

stoveyy said:


> I'm rather confident in condemning your purge valve though. A leaking purge valve will allow gas vapor that shouldn't be there to be there all the time. You'll get rich conditions and you will also get a hanging idle. Or surging idle.


Hey stoveyy, I did notice that you have a couple threads up recently about purge valves. Did you actually use this Hyundai valve on your car, and if so how well does it work? I see they sell at Rockauto for pretty cheap (if that's the same one).

Partsgeek.com has a purge valve listed under the Audi section using the last bit of the part number you provided. http://www.partsgeek.com/gbproducts/TC/18266-06011433.html

Mind looking to see if that's the same one? I have a friend who's going to let me pick up a valve off him for a few bucks since it's high mileage, but I figure why not try it to see if anything changes anyway.

Kei

*Also can the valve be cleaned?*


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## dmsonik (Feb 16, 2011)

I think your next step should be a compression test. I've been through the same scenario with a similar setup. I did a compression test which led me to pull apart my head, and found two bent valves, and pieces of springs.....:sly:.....


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## Kiyokix (Dec 16, 2005)

dmsonik said:


> I think your next step should be a compression test. I've been through the same scenario with a similar setup. I did a compression test which led me to pull apart my head, and found two bent valves, and pieces of springs.....:sly:.....


I have no doubts my compression is just fine, but I appreciate the reply.
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As for the purge valve I was going to test today...it wasn't in good enough condition to try out when I tried to pull it off one of the ends snapped with little force. Oh well, I'll get it sorted soon enough lol. I did replace the intake hose, and a few other little things just because they were cheap.

Kei


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## stoveyy (Aug 18, 2007)

Its the exact same valve. Works without a problem. They look exactly the same and ohm out the same. Both are NC.


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## Kiyokix (Dec 16, 2005)

Thanks a lot stoveyy, I'm going to see if I can't scrape together some coin to pick one up really soon like. (money just got _super_ tight, but hopefully it works out)

Any other ideas from anyone please feel 100% free to keep on posting them up! I'll update as I check things on the car, and let you guys know when it's running strong again. 

Kei


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## Wes.Drelleshak (Feb 19, 2011)

Your short and long term fuel trim is to lean. The car is tring to correct itself by adding fuel. 

Do you have a scanner that reads short and long term fuel trim? 
If so hook it up and start the car let idle. Use a can of brake cleaner and lightly spray around your t-body, intake gaskets, and valve cover gasket. Watch the short term fuel trim to see if it heads towards the positive, if it does your chasing a air leak. 

Make sure to have a fire ex around and spray away from the coil pack or dist.


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## stoveyy (Aug 18, 2007)

Wes.Drelleshak said:


> Your short and long term fuel trim is to lean. The car is tring to correct itself by adding fuel.
> 
> Do you have a scanner that reads short and long term fuel trim?
> If so hook it up and start the car let idle. Use a can of brake cleaner and lightly spray around your t-body, intake gaskets, and valve cover gasket. Watch the short term fuel trim to see if it heads towards the positive, if it does your chasing a air leak.
> ...


You've got it backwards. Cars running rich and the PCM is pulling fuel. Negative fuel trim is pulling or a rich condition. Positive is a lean condition. 

I'm still betting its a bad purge valve


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## Kiyokix (Dec 16, 2005)

stoveyy said:


> You've got it backwards. Cars running rich and the PCM is pulling fuel. Negative fuel trim is pulling or a rich condition. Positive is a lean condition.


Correct the car is running rich as we stated earlier. Wes, I appreciate the help though but you were backwards on that one. The black exhaust tip, black spark plugs, and lower fuel economy are dead giveaways to the rich condition. :thumbup:

As for chasing vacuum leaks I seriously doubt that it has anything to do with it. I've replaced almost literally every hose under the hood with new lines since they're all at least 12 years old. All of the major ones I've replaced whether or not they were good. I even replaced the stock intake tube with another one that was basically factory perfect, just so that it wouldn't be an issue that I'd overlook which is very likely when chasing vacuum leaks.

Thankfully it's not running PIG rich like it used too, so my fuel economy is still roughly 28mpg combined city/hwy as of my last three tests.

I'm _hoping_ to be able to order a new purge valve to see whether or not that's the problem this week. :thumbup:

Kei


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## Wes.Drelleshak (Feb 19, 2011)

Sorry guys,:screwy:
I guess I should have looked up the code before I opened my mouth. I was thinking of p0171 and p0174 codes and not your p0172.:banghead:

good luck on this one. Hopefully the purge valve works.


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## stoveyy (Aug 18, 2007)

Are you local to central nj? I have a brand new one you can try out


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## Kiyokix (Dec 16, 2005)

nope, wish I was but I'm about 2.5hrs away from you. 

I really appreciate the offer though :beer:

Kei


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## stoveyy (Aug 18, 2007)

I think I can get a valve from work for like 26 bucks. It'd be another 4 or 5 to ship your way. Lemme know


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## Kiyokix (Dec 16, 2005)

I let you know probably tomorrow pending sale of one of my other parts. :thumbup:

Kei


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## stoveyy (Aug 18, 2007)

It's easy enough to just see if yours is bad. Try and blow threw both sides. If it is. Your beat.


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## Kiyokix (Dec 16, 2005)

I tried that the other day, and i couldn't blow through either side...but i didn't try to blow my lungs out either.

Which side would you normally be able to blow through if it was good?

Kei


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## Kiyokix (Dec 16, 2005)

Okay so i took the valve off again today, and I blew through both ends hard enough for me to see stars....no matter how hard I blow nothing is coming through.

Kei


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## stoveyy (Aug 18, 2007)

Hmm. I'm not positive of the side. You can't say for aure what it is without a vacuum pump. It should hold vacuum one way and not the other. I couldn't blow through mine but It wouldn't hold vacuum. Thats why it took me so long to fix. I finally sucked it up and apent the 30 bucks on a vacuum pump from autozone.


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## Kiyokix (Dec 16, 2005)

*Update*

Okay so I ran the valve a friend lent me, and it seems my original evap system is functioning properly. With the valve that I installed to test with I got the P0440 code for an evap system problem. Of course the possible reasons the code comes up are indeed a faulty purge valve.

So my original valve must have been working just fine since the code didn't pop up UNTIL I put in the other valve which was slightly different pressure wise to the stock one. This is the first time I have had that code so I'm going to move on from the evap testing, and look elsewhere in the car.

I wasn't able to get the freeze data today, but the CEL did come back on with the following codes this time...

*P0141
P0440*

I know the 0141 code is for the secondary oxygen sensor since I don't have one installed in the car at all. I also don't have a cat (it was clogged so I replaced it with the 42DD test pipe until I get the money for a new one), and I couldn't get the old sensor out so I just plugged it. I have a chip that deletes the input from the sensor, but I still have to have one plugged in thus the code.

The 0440 code is of course because of the purge valve I was testing in place of the original valve. I've already put my original back in the car so that should go away when I clear the codes next time.

The P0172 rich bank 1 code DID NOT come back for whatever reason this time...

The other night I did decide to take some tb cleaner, and run it through a vacuum hose ala seafoam/water style. I didn't have any more seafoam or carb cleaner so I figured to just go with that. I was hoping to clean the motor out a bit just incase that was the cause of the rich condition. I don't know if it fixed it or not, but either way the code didn't come back...yet. I'm going to try to get the fuel trim data again maybe tomorrow, to see what if any changes there were. I haven't done ANYTHING ELSE to the car besides running the tb cleaner through the vacuum hose while it was running to try to clean it out.

I still don't have full power so I know that all is not well, I picked up another throttle body from a friend to try it out. Thank God for friends with extra parts laying around to try out on my car. It would suck to have to buy a bunch of parts just to find out you didn't need it lol. 

I'll let you guys know what happens next....

Kei


(of course keep firing ideas if you have any I haven't tried)


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## Kiyokix (Dec 16, 2005)

*UPDATE to the update lol*

Okay so I swapped throttle bodies to see if it made a difference....of course not. So back to the drawing board to see what to test next. Why oh why couldn't this just be a simple 'hey i'm broken' thing. :banghead:

Kei


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## electric-booat (Jun 22, 2005)

omg I'm having the same problem with me vdub. The car idles a little rough but not full blown misfire (wrx sound lol) and the engine seems to be sluggish upon acceleration. My brothers mk4 2.0 seems like a race car compared to mine. The exhaust smells of a rich mixture and driving 15 miles burned 1/16th of my tank. 

VAG-COM Version: Release 311.2-N


Chassis Type: 1H - VW G/J/V Mk3
Scan: 01,02,03,08,15,25,56

Address 01 -------------------------------------------------------
Controller: 037 906 259 R 
Component: MOTRONIC M5.9 HS V01
Coding: 00000
Shop #: WSC 00066
5 Faults Found:
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - - Intermittent
16686 - Cylinder 2 Misfire Detected
P0302 - 35-10 - - - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - - Intermittent
16686 - Cylinder 2 Misfire Detected
P0302 - 35-10 - - - Intermittent
16556 - Fuel Trim: System Too Rich: Bank 1
P0172 - 35-10 - - - Intermittent
Readiness: 0000 0000

Skipping Address 15-Airbags

End -------------------------------------------------------


Which measuring blocks do I use to look at the fuel concentration on vag com 311?


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## Kiyokix (Dec 16, 2005)

*Update*

I'm putting in a call with ATP/UM to find out whether or not it's just a bad chip burn or something. Other than that it simply doesn't make any sense with all the stuff I've tested/cleaned/swapped/replaced new.

I really wanna have this thing sorted out before I finally hit the big 200k mark which is is 1,057 miles. :thumbup:

Kei


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## refused1090 (Sep 21, 2008)

did you ever figure it out im having the same problem and the only other mods i have done to my car is a 260 cam and the heads been milled 400ths of an inch. was your c2 chip the race file to?


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## Kiyokix (Dec 16, 2005)

Nope, I still haven't figured this one out yet. My chip is the stage 1 version as I'm on the stock cam. I've been busy at work lately (which is awesome!) so I haven't had time to dig into it in a bit.

Another suggestion that was given to me is that there may be a leak after the throttle body, so once I get the chance I'm going to start hunting again. :thumbup:

Kei


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## refused1090 (Sep 21, 2008)

if you haven't already check your intake manifold for cracks mine was torqued down to the bently manual specs to and it still managed to crack where the upper and lower manifold meet. the easiest way to find it is with carb cleaner and listen for the idle change, but if your manifold is painted it will take off the paint. Also try to test it when you just started your car cause carb cleaner is flammable.


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## Kiyokix (Dec 16, 2005)

Thanks a lot, I didn't think about any cracks in there. I've taken it apart about a thousand times before (just the upper) so even though I've got new gaskets for it, that could very well be a problem...and why it's seemingly impossible to find the problem. 

Kei


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## retoropak (Jun 30, 2007)

Hey im chasing the same problem on my 96 cabrio
I got 270 cams no cat and PEM chip
Its throwing p0172 on that chip however it doesnt throw any codes on a stock chip.
I replaced most of the fuel air mixture related parts with no luck.
I pump the intake with 80 psi and couldnt hear any leaks.
Car acts realy strange when sitting in traffic for longer time especially when it is hot outside. It starts bogging and tries to die. 
Did you check your injectors??? They may be leaky.
Let me know if you found the problem.


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## Anony00GT (Mar 6, 2002)

Your purge solenoid is probably bad, hence the reason the rich code didn't return after you replaced it with one your friend lent you.

You stated that the new purge valve you tried was "slightly different pressure-wise" than your original...care to elaborate on that statement? I'm thinking your test valve either caused the code because of that, or it was faulty electrically. I bet a new purge valve, the proper one for your vehicle, will fix the problem.


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## gtiswapped96 (Dec 6, 2009)

Pm sent duuuuude


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## gtiswapped96 (Dec 6, 2009)

retoropak said:


> Hey im chasing the same problem on my 96 cabrio
> I got 270 cams no cat and PEM chip
> Its throwing p0172 on that chip however it doesnt throw any codes on a stock chip.
> I replaced most of the fuel air mixture related parts with no luck.
> ...


 Pm sent dude


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## The Big V (Jul 11, 1999)

KEI - what ended up happening???

i have a c2 chip and was getting the p0172 code as well immediately after installing the chip on a stock aba motor...revs were hanging...got a p0605 pcm rom error code as well...then car wouldnt start until three or four cranks last week so put the stock chip back in (a month after initially installed c2 pem) and now getting misfires even after cleaning plugs and putting injector cleaner in the fuel...!?!? thinking its several different problems but not exactly sure a lot didn't stem from the chip. gonna check MAF and ignition coil as it was raining last night when problems arose. ahhh fun. and ps-Kei...i'm at 214k miles now!


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## gtiswapped96 (Dec 6, 2009)

just keepin u guys updated....swapped in a brand new oem maf from gap.com and still got the 
p0172 code....wtf....anyone else care to chime in?


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## The Big V (Jul 11, 1999)

PMed ya Kiyokix regarding BFI getting in touch with you


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## Jetta< (Nov 14, 2013)

Bringing it back from the dead. Im having the same problem anyone figure it out? Ordering new purge valve today


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