Help me diagnose my jetta

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
I recently purchases a 2002 vw jetta gls tdi for my first car, i don’t know much ab diesels or mechanic work so this was gonna be my introduction and what i would figure stuff out on, anyways the car doesn’t idle rough until it’s on for 5-10 minutes or so then it starts to almost bog out for a second which triggers it to try and correct the stutter, also when i rev it and when dropping rpm’s it almost bogs out for a second or stutters, kinda like if fuel was completely shut off for a second on deceleration, i have a couple ideas on where to start looking, first would be the egr but i only have a basic understanding of the engine and where stuff is located, i don’t know how i would check the egr tho, second would be the injectors i’ve read tht dirty or even faulty injectors make a car idle rough but again i don’t know how i would check them, third would have to be a vacuum leek but i don’t know which to look at? can anyone help or comment on this? (i have a video of it but i don’t know how to post it in this forum)
 

John Wesley Hardin

Veteran Member
Joined
Aug 28, 2022
Location
Rockport Texas
TDI
2003 VW Jetta 1.9 Diesel GLS , Five Speed Standard Shift
Well you landed on the right site. There is a lot of knowledgeable folks here that can put you on the right path. Also general info on the site can help you identify common problems and maintenance issues.
 

STDOUBT

Veteran Member
Joined
Jul 30, 2007
Location
Portland, effing Oregon
TDI
dos jettas
Welcome to TDI Club!
Everything you need to know about the care and feeding of your amazing car is on this website.
I recommend starting with the stickies at the top of the TDI 101 forum and the VW MKIV-A4 TDIs (VE and PD) forums.
I also recommend (initially) spending FAR more time READING about your car than dinking around with it mechanically until you understand all the little quirks and got-yas.
Forging ahead with a "repair" without really understanding the procedure IN-FULL can easily result in catastrophe.
 

STDOUBT

Veteran Member
Joined
Jul 30, 2007
Location
Portland, effing Oregon
TDI
dos jettas
Now regarding the bogging-down after running 5-10 minutes.
How many miles on the car, and do you have any maintenance history records?
Is it a manual transmission?
At 5-10 minutes is your temp gauge straight up at 190?
If it was mine and was new to me, I would be thinking a fueling issue.

Why did the seller sell it? Timing Belt due? That's a big job that most places charge too much to perform, and generally do a bad job on anyway. Be aware you have bought a "hobbyists" car. Meaning, if you're not willing to do all the things to keep her on the road yourself
you might not want to spend the time and money required for that. Most VW techs don't know these cars. They are RARE here.
Generally, on these cars used, you'll want to dump another ~2,000 USD into them to get them up to snuff. And that's doing the work yourself.

Also, unless I had a trustworthy maintenance history, I would go about changing all fluids and filters, and timing belt as job 1.
That alone could possibly resolve your symptoms.
Another thing to think about is are you committed enough to spend a couple hundred bucks on the best diagnostic tool available for your car? VCDS will pay for itself if you plan to keep the car for even a few years.
Again: Read, read, read. Get to reading.
 

STDOUBT

Veteran Member
Joined
Jul 30, 2007
Location
Portland, effing Oregon
TDI
dos jettas
One more thing that should be mentioned for a fellow new to the TDI is that the RPMs should be kept at ~2500 MAX until the engine is warmed up. You do NOT want to "get on the throttle" until full op temp is reached. Once the temp gauge has risen above the 3 little hash marks, then let 3k rpm be the top for shifting. After full temp is reached, give her the beans all day! But no need to redline. Let maybe ~3600 rpm be the top until you've really got her in shape.
Most new people are surprised to learn that granny-driving a TDI is the fastest way to kill its turbo. Gets coked up unless you go Italian on the engine fairly regularly. These engines LOVE to work hard, and pretend they're sports cars. Treat it like a race car. But only after it's heated up! Learning to drive these correctly is one of the smaller hurdles. They are not gassers.
 
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AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Yes, OP, welcome to the TDI Club.

As already posted, do some research here. The Sticky section at the top of TDI 101 is an excellent place to start.

The shudder issue is due to fueling. The fuel quantity needs to be adjusted. You need Vag Com Diagnostic Systems (VCDS) as STDOUBT suggested. Without VCDS you will be lost trying to diagnose and service your TDI. With VCDS, you can adjust the fueling quantity. However, there is a limit. If adjustment with VCDS doesn't fully solve the problem, there is another option. It is called the Hammer Mod. There is at least one detailed Thread in the Sticky's in 101 that can provide you with a ton of information. It is an easy procedure but following the instructions is quite important. So, together with VCDS and the Hammer Mod, you can fine tune the idle fueling quantity for that perfect idle or slow-down idle.

I agree with the bit about history. But, history truth comes from the previous owner(s). Can you trust it? Is it worth the gamble to trust it?

Changing the Timing Belt is not for the novice. You need the proper tools and a good safe place to do the job. There is at least one Sticky on the procedure. If you do not have a Bentley Manual, you must rely on information about procedures, bolt torque specs, etc., to do the procedure properly. If you screw-up, you can destroy the engine.

Changing fluids. I'd do it in this order.

- Engine oil
- Transmission oil (is it a 5-speed or automatic)
- Coolant (personally, if the coolant is bright pink or lavender, I'd be a bit hesitate to change it).
- Power steering
- Brake fluid ......... (research)

Note: The Hammer Mod is located in TDI 101, HOW TO and do-it-yourself threads, FUEL/OIL/COOLANT RELATED.
Go there and find it ...... read.
 

jmodge

Top Post Dawg
Joined
Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 w/.205's 5speed daily summer commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/.216's winter cruiser, 1996 Tacoma ALh
Before you throw any parts at it, invest in VCDS from Rosstech. VW specific scan tool, inexpensive compared to its versatility.
I would start cheap and easy when it comes to troubleshooting. Check for air restrictions in the intake tract. Filter, snowscreen, stick ASV. Google the procedures as well as how to change the fuel filter and repriming if necessary.
 

John Wesley Hardin

Veteran Member
Joined
Aug 28, 2022
Location
Rockport Texas
TDI
2003 VW Jetta 1.9 Diesel GLS , Five Speed Standard Shift
One more thing that should be mentioned for a fellow new to the TDI is that the RPMs should be kept at ~2500 MAX until the engine is warmed up. You do NOT want to "get on the throttle" until full op temp is reached. Once the temp gauge has risen above the 3 little hash marks, then let 3k rpm be the top for shifting. After full temp is reached, give her the beans all day! But no need to redline. Let maybe ~3600 rpm be the top until you've really got her in shape.
Most new people are surprised to learn that granny-driving a TDI is the fastest way to kill its turbo. Gets coked up unless you go Italian on the engine fairly regularly. These engines LOVE to work hard, and pretend they're sports cars. Treat it like a race car. But only after it's heated up! Learning to drive these correctly is one of the smaller hurdles. They are not gassers.
Good advice thats what I do now slowly warm it up ,once its up to temp look out you freaks!
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
thank you all for all the tips i appreciate it a ton right now i’m in the middle of clutch assembly rebuild so my tranny is out and slowly getting the parts it need delivered, also every time i’ve reved it i only go to 3500 max and let it heat up to 190 or more which is as hot as it’s getting in this cold wether, i’m understanding tht before i do anything to the engine i should check up with the ecu via vcds an get tht all as perfect as possible, then most likely change oil , coolant , fuel filter/oil filter (lmk if i’m missing something),
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
i was thinking on building and engine on the side i have everything in my notes from manifold , injectors, injector pump , fmic , arp head studs , arp main caps , stage 3 camshaft , dual valve springs , cam lifters , tubular manifold. for turbos i have no clue what would be over kill but i am looking for horsepower so i was thinking a GTB3073VKLR by PRODIESEL, would that be over kill i’ve only bin looking at what you would need to build the block like max speeding rods connecting rods and i haven’t found any pistons or any way of building the pistons also where would i take my head polished and valves bored out?, again all the help is appreciate a ton.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
My car had this kind of stutter recently and I was convinced it was a fueling issue. It wasn't: the N239 valve was shot and letting the ant-shudder valve close occasionally. New N239 and problem was solved.
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
thank you all for all the tips i appreciate it a ton right now i’m in the middle of clutch assembly rebuild so my tranny is out and slowly getting the parts it need delivered, also every time i’ve reved it i only go to 3500 max and let it heat up to 190 or more which is as hot as it’s getting in this cold wether, i’m understanding tht before i do anything to the engine i should check up with the ecu via vcds an get tht all as perfect as possible, then most likely change oil , coolant , fuel filter/oil filter (lmk if i’m missing something),

the clutch was destroyed so i got it fairly cheap, and it has around 2xx,xxx miles on motor and chassis as for the maintenance history all i know is tht the timing belt was done before, it has a 5speed and i’ve not bin able to test drive it , other than the tranny and the fueling (my guess for issue is fueling) issue the engine is sounding and seeming in good condition, i’ve bought an egr delete and vcds to insure that i figure out the issue if not i will start changing fluids/filters n hope thtll fix it.

again all you guys help is very appreciated
 

braddies

Veteran Member
Joined
Jul 26, 2021
Location
America
TDI
03 golf ALH
Maintenance before modifications...
But, if it's broke, might as well upgrade.

How long ago was the time belt done? Supposed to be every 100k or (8?) years or so.
Also maybe an easy little check-it-out project would be to pull the EGR/ASV off of the intake and see how much build up is in there, the intake manifolds can get seriously clogged.
Air bubbles in the fuel line?
I'd make sure the intake path is clear and the bubbles in the fuel line are minimal before changing any settings in the ECU with vcds.
That's a sweet to-do list of power mods, but probably best to get everything sorted out "as-is" first, and get it running well
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
i fully agree my only issue is how do i figure out if there are bubbles or not and if there is how would i take them out? would it be like bleeding brakes or clutch or would i have to buy a tool to suck or push the air out?
 

csstevej

Top Post Dawg
Joined
Aug 12, 2004
Location
north nj
TDI
2001 golf tdi 4 door auto now a manual, mine, 2000 golf 2 door M/T son's,daughters 98 NB non-TDI 2.0, 2003 TDI NB for next daughter, head repaired and on road,gluten for punishment got another tdi 2001NB,another yellow tdi NB
There should be a section of clear hose between the fuel filter and the IP , that’s where you’d see the bubbles.
Most of the time it’s caused by the thermostatic tee that sits on the fuel filter, the set up isn’t the great and leaks through the two orings there.
Most times replacing the orings will fix the air bubbles but if you do it , really lube it well/excessively with Vaseline when you reinstall it. It will help plug any small defects. If you fix the leak the bubbles will self clear themselves out of the line.
 

ZippyNH

Veteran Member
Joined
Apr 22, 2015
Location
Southern NH
TDI
2015 JETTA TDI SE
Diesel fuel unfortunately is a great solvent... destructive to rubber and plastic. Have known more than one HD truck with unsolvable engine issues that it turned out to be simple fuel line issue...so many truckers proactively change out the low pressure fuel lines as a doing MAJOR work...they are litterly so cheap, it really just a labor issue. Air bubbles can cause havoc.
On VW, lift pumps in the tank(provides head pressure to the HP engine pump so it not trying to suck it from the tank) seem to be a more common issue. Just figured I would mention it before you get too deep...all easy things too look at and check
 

AndyBees

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Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
The OP's vehicle is an 02 Jetta with the ALH engine. Unless someone installed a lift pump in the tank, it doesn't have one.
All new fuel filters "should" come with two small replacement O-rings. When installed properly, there shouldn't be any air leaks. However, the internal mechanical suction pump in the Injection Pump is very strong and can move a lot of fuel. So, any restrictions in the system back to and including the pick-up unit in the tank can cause air to be sucked into the system.
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
i was planning on getting a lift pump for my tank as i do wanna eventually build an alh for sum power, however about the lines i was thinking about giving it a refresh and replacing every line but in my case as soon as i get the car running i’m going to go pick up another alh engine with some stuff done to it so the current engine doesn’t need to be 100% restored.
i’m here for opinions and thoughts so any ideas will help
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
i realize now that even if i use a different engine i would either have to get new lines anyways or reuse my old one.
for now i’m thinking of keeping my current lines until i get my engine build ready then i’d prolly slap on sum new ones when it’s ready to go in.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
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Aug 16, 2004
Location
South of Boston
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'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
The fuel lines that run from the firewall under the car to the fuel tank aren't prone to leaking or failure. I've never had to replace them on any of the 15 TDI's I've owned. They hold up well, unless someone has run WVO (not biodiesel) in the car.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Yeah, I cannot imagine why you would want to replace the fuel pipes between the fuel filter and the fuel tank. They can be blown out with compressed air. They can be tested with vacuum.

A Lift Pump will not make your ALH TDI engine run faster or have more power. A tune will. A tune with upgrades such as, bigger nozzles, VNT17 Turbo, 11mm Injection Pump Head, exhaust mods, etc.
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
hey back on my thread. so everyone was right, there is air feeding into the engine through the fuel lines, it’s visible when revving through the filter to pump see through hose.
it’s very noticeable tht it’s mostly when it’s revving.
a week before cleaning the injectors i whent on vcds and lowered injector quantity a little and the misfire in the idle where mostly if not completely gone,
after cleaning the injectors today the idling and engine/injector noise was reduced by a lot, it revs better sounds better but the it still bogs and rough idles a bit i haven’t touched the IQ after cleaning

obviously or most likely it’s the air in the fuel line i ju don’t know which to look and how to even check them, is there a easy way to check them, should i just replace most if not all lines or just any related information would help.

tomorrow i will check my tank for leaks or anything tht would allow air into the tank

another thing i am replacing my radiator fans would they come out through the top or would i have to take out everything in the way?
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
I would not replace the fuel pipes between the fuel tank and the fuel filter. I would vacuum test them. If they hold a vacuum, well, that rules-out an air leak in those sections.

As for the tank, fill it up full (Vented). In case you are not aware, look inside the fill hole... you should see a thingy sticking out about 1/4 inch. If you push with the fill-nozzle it will bleed air out of the tank as you top it off. I can typically put in another two gallons after the pump handle kicks-out by using the air vent bleeder. Then, with that full tank of fuel, see if you have air in the hose between the fuel filter and the Injection Pump. If not, well, the problem could be in the tank (which I seriously doubt). The connection on top of the fuel tank might be the culprit (key word, might).

But, my money is on the Thermostatic T on top of the fuel filter. That T has two O-rings that just do not seal very well at all. They are the cause of the majority of air infiltrating into the fuel system. The good thing is, that air is filtered... LOL.

Those Fans go out the bottom much easier. It is easier to work from the bottom because the plug/connectors are down there. Four screws and two connectors... the whole thing will come out. Or, you can take them out individually... three screws each and the same two electrical connectors.
 
Last edited:

csstevej

Top Post Dawg
Joined
Aug 12, 2004
Location
north nj
TDI
2001 golf tdi 4 door auto now a manual, mine, 2000 golf 2 door M/T son's,daughters 98 NB non-TDI 2.0, 2003 TDI NB for next daughter, head repaired and on road,gluten for punishment got another tdi 2001NB,another yellow tdi NB
What Andy said.
You can replace those two o-rings on the thermostatic, and if you do liberally apply petroleum jelly on them before installing them , it will help with installation and plug up any irregularities.
 

jokila

Vendor
Joined
Dec 3, 2004
Location
Houston, Texas
TDI
2003 Jetta GLS, Manual
One more thing that should be mentioned for a fellow new to the TDI is that the RPMs should be kept at ~2500 MAX until the engine is warmed up. You do NOT want to "get on the throttle" until full op temp is reached. Once the temp gauge has risen above the 3 little hash marks, then let 3k rpm be the top for shifting. After full temp is reached, give her the beans all day! But no need to redline. Let maybe ~3600 rpm be the top until you've really got her in shape.
Most new people are surprised to learn that granny-driving a TDI is the fastest way to kill its turbo. Gets coked up unless you go Italian on the engine fairly regularly. These engines LOVE to work hard, and pretend they're sports cars. Treat it like a race car. But only after it's heated up! Learning to drive these correctly is one of the smaller hurdles. They are not gassers.
I recall from years ago on this site where you would go 2500 max until the temp gauge got above the first three "bubbles" of the temp gauge. Then, you would limit to 3000 rpm until fully warmed up.
 

T1MMBOJONES

Veteran Member
Joined
Nov 10, 2020
Location
Milwaukee
TDI
03 ALH 01M wagon
i bypassed a lot of comments, so sorry if this has been mentioned, but i would do a fuel filter before diving any deeper unlike a gas engine these need changed regularily and can cause multiple problems that tend to seem like other issues....
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
i bypassed a lot of comments, so sorry if this has been mentioned, but i would do a fuel filter before diving any deeper unlike a gas engine these need changed regularily and can cause multiple problems that tend to seem like other issues....
I'm not disagreeing with your comment. It is a good suggestion and I don't think the OP has mentioned changing the fuel filter. However, several of us have suggested that he change the two O-rings on the Thermostatic T on the fuel filter.

Anyway, I'd like to share these three stories about fuel filters.

1. My brother was the first in my family to buy a TDI (2001 Jetta). Although I had been driving VW diesels since January, 1980, I had resisted buying a TDI until he got his. I drove it and was definitely impressed. So, I stumbled onto a low miles 2000 Jetta in March, 02. (my son owns it, now has 399k miles)

Anyway, my brother has always lived at least a half day's drive or more from me. One weekend while he was visiting, we tinkered on our TDIs. I ask him how often had he been changing the fuel filter. He said he had never changed it. Well, believe it or not, the OE filter had 171,000 miles on it. He said he had not had any issue about starting and running. So, obviously we did a fuel filter change.

2. During my career, I was driving no less than 36k miles per year which involved commuting to work and on the job driving. I only changed the fuel filter once per year. I did it anywhere from mid-November to mid-December so it would be fresh for the winter.

3. I've done maintenance on a 2001 Jetta since about 2008. The individual brought the car to me for a TB job back in November. I looked up records to see the last things I had done. I was surprised to see the air and fuel filters had over 55k miles on them.

So, yes, they should be changed around 20k miles.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Fuel filter life depends on the quality of fuel you're using. I've had fuel filters clog with biodiesel, water from a low tank, and debris from a tank where the fuel has set. If you don't encounter these issues the filter may last a long time.

I've also driven to track events with the car running fine, but when I wanted to use full power it would not deliver. A fresh fuel filter fixed the issue more than once.
 

T1MMBOJONES

Veteran Member
Joined
Nov 10, 2020
Location
Milwaukee
TDI
03 ALH 01M wagon
i guess comming from a duramax plaqued with injector problems 20k is my interval
on fuel filters in all my current and past diesels no exceptions. easy enough and ALWAYS the first thing i do when purchasing a "new" one. like i said i only briefed this log but wanted to stress its importance to a new owner....
 

n0.j0y

Active member
Joined
Jan 19, 2024
Location
connecticut
TDI
2002 jetta gls tdi
thank you all the fuel filter was the issue a week ago i replaced the filter and T with new O rings and everything is perfect and running mint.

now i have two issue on my hands,
i can’t pass emissions because and i quote catalytic converter (VISUAL) result, i need it to pass so i was wondering if they only have to see it, would it be pass with a cut up a cat and wrap it around a part of my straight pipe everything else is fine, i’m hoping i won’t have to reinstall a factory exhaust on to it.

other problem is my transmission previously i fixed the the destroyed clutch and clutch lever i also bought the bearing, it runs and drive good enough but there two major issue every time i let go of the clutch wether in neutral or moving the trans making a clanking sounds i have an idea of what is happening in there but is it fixable is my question, next ties in with the ****ed trans, everytime i’m in gear the transmission likes to slightly holds the rpm’s n then stutters it’s more noticeable at lowers speeds.
i honestly think i just need a new trans and some good axles
 
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