22 MPG??

matttdi

Well-known member
Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
So as the title states, i’m averaging 22MPG in my 2004. I have an EGR delete, CAI, straight pipe, and an upgraded turbo (VNT17) without a tune, but when I first got it I was averaging 50MPG reliably.
(Sorry in advance for the long post)

I first noticed this change after my dogbone motor mount broke in half, replaced it (without driving it more than 2 miles very gingerly), and now i have a bit of white smoke on startup from under the hood and also out the exhaust. I did an oil change and added Liqui-Moly motor oil saver, but this didn’t really change anything. It runs incredibly smooth other than on a startup, when it studders and smokes for less than 30 seconds and then runs fine. On top of all this, occasionally my veins will stick on a cold start, but if i turn it off and back on while driving it immediately fixes the issue (this has been happening since i bought it). I’m kinda stumped as I can’t really tell where to start here since I was getting fine mileage before the dogbone, but not after, even though I looked around to try to make sure nothing else was broken. If anyone has any suggestions on how to tackle this please let me know, but i don’t want to just throw parts at it without reasonable explanation. Thanks in advance!
 

Nero Morg

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Oct 19, 2017
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OR
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2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
What CAI did you do? General consensus is that the stock intake system is plenty good and is already a cold air intake. May be getting hot air which would throw off your fuel tables.

Another thing to check is if something was damaged when your dog one broke. All that engine swinging, make sure your vacuum lines are good and sensors undamaged. Amy fault codes?
 

matttdi

Well-known member
Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
What CAI did you do? General consensus is that the stock intake system is plenty good and is already a cold air intake. May be getting hot air which would throw off your fuel tables.

Another thing to check is if something was damaged when your dog one broke. All that engine swinging, make sure your vacuum lines are good and sensors undamaged. Amy fault codes?
Going to get the codes read right now, as I don’t have my scanner with me. Everything that’s done to the car was already done when i bought it unfortunately, including the no name CAI.
 

Tdijarhead

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2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Wife’s car, 2005 Golf TDI Mine, all 5 spds
I've thought about this whole CAI thing, I don't have one by the way. I understand the idea is to draw cold air in to increase horsepower. All the CAI's I have seen pics of just lay in the engine bay and suck the hot air from off the top of the engine, whereas the stock air intake draws air in a tube from around the headlight area. That seems to me the aftermarket CAI's are really more of a Hot Air Intake as opposed to the stock unit which draws air from in front of the car.
 

Mongler98

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Mar 23, 2011
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COLORADO (SE of Denver)
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98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Calling out maf issues.
Scan and see what the map is doing.
 

matttdi

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Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
I've thought about this whole CAI thing, I don't have one by the way. I understand the idea is to draw cold air in to increase horsepower. All the CAI's I have seen pics of just lay in the engine bay and suck the hot air from off the top of the engine, whereas the stock air intake draws air in a tube from around the headlight area. That seems to me the aftermarket CAI's are really more of a Hot Air Intake as opposed to the stock unit which draws air from in front of the car.
not to be a dick but this has nothing to do with my original question.
 

matttdi

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Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Calling out maf issues.
Scan and see what the map is doing.
So it seems you may be right about the maf, it’s reading P0101, P0236, and P0135 on top of the EGR code. Could the maf code just be from the CAI? Or should I go ahead and replace it to be safe?
 

Nero Morg

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OR
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2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
Depends. Tdijarhead had a good point, sucking in hot engine air will cause the fuel tables to lean out which will affect fuel economy. If it's an oil soaked air filter, the oils will end up on the maf and ruin it. They're very sensitive maf sensors.
 

matttdi

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Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Depends. Tdijarhead had a good point, sucking in hot engine air will cause the fuel tables to lean out which will affect fuel economy. If it's an oil soaked air filter, the oils will end up on the maf and ruin it. They're very sensitive maf sensors.
i guess you might be right, i just figured since the CAI has been on for so long that it wouldn’t just all of a sudden trip up my MAF
 

Diesel Fumes

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Joined
Dec 30, 2008
Location
Creston, bc
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2003 alh tdi 5 speed
Don't all the codes stay stored? Did you reset them and they come back? Maf sensor is a good place to check.
Weird you have the same things i have going on. Smoke at start up, limp mode etc. But I still get great fuel economy. 22mpg I'd imagine the engine would smoke like a chimney and/or constantly reek of diesel fumes (Hehe). That's a lot of fuel being burnt to move a tdi around. At least double the expected amount

I originally had bad fuel economy with my car when I bought it. Ended up being caused by sticky rear brakes. It's worth checking to see if they get hot after a drive. But otherwise it sounds like it could be many things and I hope you find your answer here
 

matttdi

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Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Don't all the codes stay stored? Did you reset them and they come back? Maf sensor is a good place to check.
Weird you have the same things i have going on. Smoke at start up, limp mode etc. But I still get great fuel economy. 22mpg I'd imagine the engine would smoke like a chimney and/or constantly reek of diesel fumes (Hehe). That's a lot of fuel being burnt to move a tdi around. At least double the expected amount

I originally had bad fuel economy with my car when I bought it. Ended up being caused by sticky rear brakes. It's worth checking to see if they get hot after a drive. But otherwise it sounds like it could be many things and I hope you find your answer here
yeah i actually have noticed more diesel fumes but no smoke, and I cleared the codes at advanced auto, then drove the couple miles to autozone and had them read the codes to see what is new and what’s from the previous owner that he never cleared. those codes were the only ones that popped up on that drive. i also forgot to mention that when it’s cold out and i start the car, if the AC is on and blowing, you can see smoke coming out of the vents (because of the cold weather you can see it, if it’s warm i can only smell it) but when i turn the AC off i have no smoke out of the vents. not really sure if this helps or how this even relates to anything but i just remembered.
 

Tdijarhead

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2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Wife’s car, 2005 Golf TDI Mine, all 5 spds
not to be a dick but this has nothing to do with my original question.

Maybe it does. An oil soaked CAI will ruin a MAF, usually it takes a while for the intake to suck enough oil onto the MAF to cause problems. If the previous owner had just installed the CAI or had just replaced the MAF that might explain why you got great mileage when you first got the car and now not so much.

I think it’s likely you have several things going on to rob that much mileage from your car. Brakes, MAF the 04 has a single O2 sensor. Here is oilhammer s mpg thread.

 

AndyBees

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May 27, 2003
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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Long shot: The Coolant Temp Sensor wiring is not very far from the Dog Bone area. Not knowing how the Dog Bone got broke, I ask do you know? If something from the roadway hit the DB maybe some debris broke a wire to the Coolant Temp sensor. Or, is the Coolant Temp Sensor sending a code? Typically, if the ECU info side of the Coolant Temp Sensor goes bad it will default to minus 400f which will cause the engine to run extremely rich.

I agree with the comments on the Cold Air Intake ..... the OE filter system is the best by far. And, it will not oil up the MAF.

Lastly, possibly a worn Cam ..... saw this recently with a friend's 06 with the BRM engine.
 

Tdijarhead

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Lawrenceville PA
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2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Wife’s car, 2005 Golf TDI Mine, all 5 spds
Forgot about that cam, I just replaced mine the first of October, so it should be fresh in my mind. Torsion setting can also effect mileage, however it doesn’t sound as if you’ve deliberately changed the torsion, and you were getting good mpg’s so it’s not likely that. Check your coolant temperature sensor as Andy suggested and work through oilhammer’s thread and see where you’re at when you get done.
 

matttdi

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Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Long shot: The Coolant Temp Sensor wiring is not very far from the Dog Bone area. Not knowing how the Dog Bone got broke, I ask do you know? If something from the roadway hit the DB maybe some debris broke a wire to the Coolant Temp sensor. Or, is the Coolant Temp Sensor sending a code? Typically, if the ECU info side of the Coolant Temp Sensor goes bad it will default to minus 400f which will cause the engine to run extremely rich.

I agree with the comments on the Cold Air Intake ..... the OE filter system is the best by far. And, it will not oil up the MAF.

Lastly, possibly a worn Cam ..... saw this recently with a friend's 06 with the BRM engine.
I believe the thermostat is stuck open as on cold days, the car never gets up to temp, but on a regular day like today I saw it reach the normal 190°. I believe my problem to be a mix of everything put together but the dogbone breaking remains a mystery. I parked the car, it was fine, I started it back up the next morning and it was broken. I’m going to crawl under it this week to find out if i can see anything blatantly obvious that could be broken that I missed when i replaced the dogbone.
 

matttdi

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Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Forgot about that cam, I just replaced mine the first of October, so it should be fresh in my mind. Torsion setting can also effect mileage, however it doesn’t sound as if you’ve deliberately changed the torsion, and you were getting good mpg’s so it’s not likely that. Check your coolant temperature sensor as Andy suggested and work through oilhammer’s thread and see where you’re at when you get done.
praying it isn’t the cam haha.
 

AndyBees

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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Keep in mind, the Temp Sensor has two circuits, one for the Gauge in the Cluster and the other for the ECU. I've seen them go bad on the ECU side and work properly on the Gauge side ............ a Scan with VCDS will show if either is bad.
 

Mongler98

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Mar 23, 2011
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COLORADO (SE of Denver)
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98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
So it seems you may be right about the maf, it’s reading P0101, P0236, and P0135 on top of the EGR code. Could the maf code just be from the CAI? Or should I go ahead and replace it to be safe?
its fubar. because oils and dust have collected on the element because of the crappy filtration of a non OEM filter.
congrats on causing more $ to be spent for no reason other than hood bling culture..... ok rant over.
yea that's not good. live and learn... I ran 230hp on a AHU with no tune and 764 nozzles on 27 PSI with constant limp mode when racing... didnt care still got 55mpg when i drove sane to and from work. then i got a stage 6 tune and really never left the pedal off the floor.... lol seriously
stock airbox... MANN filter...
 

Nero Morg

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Also note, Mongler, he said he bought the car with it already in there.
 

IndigoBlueWagon

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Aug 16, 2004
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South of Boston
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'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
I wonder if this is as simple as a disconnected boost hose from the broken dogbone mount. And I bet you have a broken EGR pipe. Most of these cars do when you can smell diesel.
 
Last edited:

BobnOH

not-a-mechanic
Joined
May 29, 2004
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central Ohio
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New Beetle 2003 manual
50 to 22. Something major, serious internal damage, wore out injectors, clogged or disconnected or damaged air pipes or exhaust (clogged CAT).
 

matttdi

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Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
thank you to everyone for trying to help me! i’m actually under the car right now and apart from oil buildup from 205k miles, i don’t see anything extremely wrong except for the downpipe doesn’t have any bolts bolting it into the turbo? i’m guessing these either backed out or maybe the car never had them when i bought it but there are 3 gaskets somehow still being suspended in between the turbo and the downpipe. i have the garrett vnt17, is there anywhere to buy just the bolts?
 

matttdi

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Aug 2, 2021
Location
Indianapolis, IN
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2004 Jetta
nevermind i’m mistaken, the top most bolt is still there, suspending the gaskets but still creating a gap of about a quarter inch off the turbo from the downpipe. these gaskets can rotate around the bolt that’s in place, blocking off gasses from exciting the engine
 

oilhammer

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outside St Louis, MO
TDI
There are just too many to list....
Sounds to me like the car is a butchered mess (I understand you bought it that way), and you may have a lot of things wrong.

A stock BEW, even with a manual, isn't often known to tag 50 MPGs, usually 45 or so... and if you really are getting 22, I'd think you'd be leaving black clouds behind you wherever you went.

I'd love to see some underhood pics. I bet all kinds of stuff is wrong with that poor car.
 

matttdi

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Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Sounds to me like the car is a butchered mess (I understand you bought it that way), and you may have a lot of things wrong.

A stock BEW, even with a manual, isn't often known to tag 50 MPGs, usually 45 or so... and if you really are getting 22, I'd think you'd be leaving black clouds behind you wherever you went.

I'd love to see some underhood pics. I bet all kinds of stuff is wrong with that poor car.
100% you’re right it is a mess. my first diesel and i thought it’d be a good daily, but it’s proving to be much more of a hassle than i thought. i just ordered the studs for the exhaust flange so hopefully that is a good starting point for helping my situation.
 

Nero Morg

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Well, there's a culprit. Having the down pipe missing or loose shouldn't hurt fuel economy, but with the intake you have... It's just gonna suck all that hot exhaust right back in... And since it's inert gasses.... It won't combust well.
 

matttdi

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Joined
Aug 2, 2021
Location
Indianapolis, IN
TDI
2004 Jetta
Well, there's a culprit. Having the down pipe missing or loose shouldn't hurt fuel economy, but with the intake you have... It's just gonna suck all that hot exhaust right back in... And since it's inert gasses.... It won't combust well.
yeah i’m guessing that’s the culprit. i actually noticed today on the interstate i was getting better fuel economy (i’m guessing because of the airflow though the engine bay) than compared to in the city where i do most of my driving. if the studs don’t fix the problem at all then it’s back to the garage!
 

BobnOH

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May 29, 2004
Location
central Ohio
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New Beetle 2003 manual
We forget that fuel is diesel and Air. Mess with the ration a whole bunch and you don't get a good explosion.
 

ssullivan

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Aug 23, 2021
Location
NV
TDI
2001 Jetta
I believe the thermostat is stuck open as on cold days, the car never gets up to temp, but on a regular day like today I saw it reach the normal 190°. I believe my problem to be a mix of everything put together but the dogbone breaking remains a mystery. I parked the car, it was fine, I started it back up the next morning and it was broken. I’m going to crawl under it this week to find out if i can see anything blatantly obvious that could be broken that I missed when i replaced the dogbone.
This was worth 3-5mpg for me, plus the peace of mind that the already failed thermostat isn't at risk of failing closed and overheating everything. I would double check all the boost and little vacuum hoses too.
 

Hayze

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May 30, 2020
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Oklahoma City
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2009 Jetta TDI 2.0L
Words of advice and what im currently dealing with on my 2009 TDI, There are some things i have learned over the course of doing universal aftermarket CAI setup on this car.
I do have an CAI setup for mine, yes it ran great however the MAF's on these cars are VERY sensitive.
Ive done a lot of testing with several different approaches to using CAI and discoveries while using one.

So i have an XL cone filter from spectre, (Biggest one you can get off the shelf)
also added 2 45 degree elbows as well a 90 degree elbow with maf in the middle. (perfect fit) looks nice!

Click to view large image.



However in setup such as this I have experienced the following symptoms.

- Shuttering rpm ranges between 1800 - 2100 during windy weather.
- Limp Mode - MAF air flow sensor operating above airflow parameters.
- Limp Mode will engage if climbing a hill in 6th gear on dsg, may not in 5th at higher rpms.

These cars will go into limp mode if too much air passes through the maf. They are affected by turbulated airflow as well too much airflow.

Discovery.
I do not have images of what i did to prevent turbulated airflow into the maf, however i did take the hood material from under the hood and stuffed down by the driver side headlight to avoid air flying up into the wheel well forcing airflow into the filer and maf.

Discovery road test
when driving under normal conditions, it worked fine,
Taking off under heavy load and ripping through the gears past 4k rpm will trigger limp mode after 4th gear. Triggering maf error codes.

Bottom line,
if you want to drive with CAI and operate with better fuel efficiency.
You can drive with the maf unplugged however, when its time for your car to do a regen.
Do NOT ignore the dpf filter light and continue driving with maf unplugged.
Your car will NOT do regen if maf is unplugged.
If you ignore the dpf light and continue driving after 50 miles your car will go into a stage 2 de-rate.
in other words, your car is in limp mode, but the only way you can get out of limp mode, is by using vag com and triggering an emergency regen.

REGARDLESS of how much soot level is in dpf.

So,
Find a safe place to stop,
shut car off,
open hood,
plug maf sensor back in,
start car,
wait at least 1 minute then continue on your journey.

After DPF light disappears repeat process only this time unplug maf sensor.

Do I recommend any of this? NO absolutely not,
it is a risky setup to have on these cars unless you know what your doing.

Diesels are more complicated than gas powered vehicles are.

Best thing to start with first before any CAI setup.

1. Full Emissions delete,
2. CAI setup with no MAF sensor.
 
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