1999.5 ALH Jetta intermittent idle stumble

RhysOnArrakis

New member
Joined
Apr 15, 2019
Location
Lake Ariel, PA
TDI
Jetta 1999.5 mk IV
Hello, I am hoping to get a few good opinions here on this issue that I am having. Engine will idle fine, then will act as tho misfiring for about 5 seconds, then resume normal idle. This cycle repeats anywhere from every 10 seconds to every 30 seconds, no matter if the engine is cold or warm, after a drive or initial start-up. Above idle all is normal, runs very strong. It's been doing this for a few months now, and as this is not my daily I planned to troubleshoot this time permitting. But I have no failures or DTC's per VCDS, and even a tick above idle and the problem goes away! So far the most likely culprit in my limited TDI experience is a sticking fuel injector. Any other input would be greatly appreciated. 269,000 miles, fresh EGR overhaul and intake cleaning, ALL vacuum lines replaced, all regular servicing done religiously. Thanks!

Rhys L.
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2003 Jetta wagon, 2001 Jetta TDI, 2014 Passat TDI
Sounds more like you're getting air in your fuel system. Common leak points are the thermo T on the fuel filter, and the quick disconnect lines next to the strut tower.
 

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
If you have VCDS I'd try raising the IQ (injection quantity) a bit. '99.5s experience what some people call a "slowdown shudder", especially when they're cold. It can start to appear as injectors wear and deliver a small amount of additional fuel. Bumping the IQ up a bit usually fixes it.
 

RhysOnArrakis

New member
Joined
Apr 15, 2019
Location
Lake Ariel, PA
TDI
Jetta 1999.5 mk IV
Original lifters. And while I was in looking for leaks in the under-hood fuel lines, I couldn't believe what I saw (heard). What I thought was a valve cover gasket leak was a growing diesel stain. I shut off the engine and heard hissing from #2 and 3 injectors. These injectors need to be re-sealed, yes? Just pull all 4 and put in new seals while I'm at it? After that I will start exploring the higher functions of vcds.

Rhys L.
 

Nero Morg

Top Post Dawg
Joined
Oct 19, 2017
Location
OR
TDI
2003 Jetta wagon, 2001 Jetta TDI, 2014 Passat TDI
All the fuel supply lines from the pump to fuel tank are under suction. If you have clear lines you could see bubbles for air intrusion. As for hissing noises, spray soapy water at your injectors/glow plugs where they meet the head to see if you have compression leakage.
 

RhysOnArrakis

New member
Joined
Apr 15, 2019
Location
Lake Ariel, PA
TDI
Jetta 1999.5 mk IV
Definitely injectors 2 and 3 leaking, confirmed with soapy water test. Going to get those sorted and then start changing some 20 year old fuel hoses!
 
Top