Stumbling Idle on cold start only

Mk4sochist

Member
Joined
Sep 26, 2020
Location
Washington
TDI
Mk4 Jetta
I've got a 2002 Jetta TDI (ALH) , 228K miles, stock. It recently developed an issue during cold starts. It's stumbles somewhat rhythmically at idle and produces quite a bit of white smoke for about a minute. It's not throwing any codes, and it's only on cold start. Once warm, it idles at 903 RPM and is rock solid. Now that it's getting colder out, it's definitely getting worse.

See video below. Wondering if anyone has any thoughts before I take it into a shop.

ALH stumbling on cold start
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
My car did the same thing for a few months, was a lot more noticeable because I have a fast idle warmup tuned in, where at cold temps it idles at 1100 until about 138f. Root cause was a two parter for me. Fuel return line bleeding down, and a very tiny crack in the mating point of the injector supply line for #4. Chances are yours is just the fuel return line leakage, which could be the fuel lines between the injectors, (the rubber ones) or your thermo t on the fuel filter isn't sealing correctly. I've seen the non-oem fuel filters have that hole not truly round, so it'll leak down over night. Hope it helps.
 

Mk4sochist

Member
Joined
Sep 26, 2020
Location
Washington
TDI
Mk4 Jetta
Thanks for the reply. I checked my fuel lines and noted a small air bubble in the clear supply line between the filter and the IP. I'll probably swap out those lines and go from there. I can't believe how expensive the simple fuel lines are...
 

jokila

Vendor
Joined
Dec 3, 2004
Location
Houston, Texas
TDI
2003 Jetta GLS, Manual
Thanks for the reply. I checked my fuel lines and noted a small air bubble in the clear supply line between the filter and the IP. I'll probably swap out those lines and go from there. I can't believe how expensive the simple fuel lines are...
I have seen it leak at the union of the clear line to the rubber. The ferrule that mates the two can allow air to seep in.
 
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KrashDH

Top Post Dawg
Joined
Dec 22, 2013
Location
Washington
TDI
2002 Golf
Thanks for the reply. I checked my fuel lines and noted a small air bubble in the clear supply line between the filter and the IP. I'll probably swap out those lines and go from there. I can't believe how expensive the simple fuel lines are...
A small air bubble in the clear line isn't going to affect anything. I've had one in my car since I've owned it, I'm sure it was there for the PO too. It starts and runs just fine. No pump leaks, no leaks at the fuel filter (I'm running aftermarket filter).

If you just had a fuel line leak (ie air getting in), I don't think it would cause the white smoke you mentioned, it would just cause it to start and run poorly. White smoke is raw, unburnt fuel. Could be a timing issue, could be an injector leaking down.

Timing isn't hard to verify, injectors have to be pulled and sent out for a flow test if you want to rule them out.
 

Mk4sochist

Member
Joined
Sep 26, 2020
Location
Washington
TDI
Mk4 Jetta
Thanks for the input. Injectors were on my radar, but I was hoping for something simpler. I don't have the tools for that... Looks like it's going to the shop.

I was planning on replacing the fuel lines as a precaution as they were looking a little rough on the outside on my last fuel filter change out but seemed intact otherwise. The supply lines from the fuel filter to the IP (1J0130307R) are sold out and backordered across the country. What gives??
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2014 A6 TDI, 2001 Jetta TDI, 2014 Passat TDI
Because it's a 17 year old car and dealers typically only keep current and last Gen parts on hand.
Your best bet is IDparts, wrecking yard, or private/for sale on the forums here. I don't think it's the lines from filter to injection pump though.
 

Mk4sochist

Member
Joined
Sep 26, 2020
Location
Washington
TDI
Mk4 Jetta
IDParts is sold out (part is on order), as are other online OEM retailers. I can't find a store anywhere that has those lines in stock. I'm not tackling this myself. Taking to my shop on Wednesday.
 

Nevada_TDI

Top Post Dawg
Joined
Aug 17, 2008
Location
Reno, sort of...
TDI
2001 Jetta TDI
It is really easy to pull the injectors out to send the them to Franko6. With a steady hand, a 15mm socket and a 17mm open end wrench, you can usually get the injectors to pull out. I am not suggesting you do exactly this: if the nut on the top of the injector has been loosened, and the 15mm nut on the clamp has been loosened there is a spot on the outside of the injector body the an open end wrench will fit onto. If the injector body seems to be able to move back and forth with the slightest amount of force applied, then the injector will likely come out easily. If the injector does not want to move, don't add more torque, call it a day and find someone, a TDI Guru if possible.
 

zslnk

Veteran Member
Joined
Sep 4, 2006
Location
ON, CANADA
TDI
E320 CDI, 3rd gen Cummins 2500, ALH Sedan
I made a puller from an auto body slide hammer tool. One nut that fits the injector body and one nut that fits the puller. MIG weld together. It works very well.
 
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