Intermittent limp mode

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
I've read quite a few threads here from search results on this matter, but none of them specify my issue. My car: 1998 Jetta TDI 5spd with 279k

This happens when the ambient air is around 15 degrees. The car is going great, as usual then it feels like it's losing fuel pressure suddenly and power is reduced. I thought this could be bad fuel or a dirty filter, so I cycled the ignition while I was going down the highway and it runs great again for a mile, maybe 10. This is on my way to work in the morning, but on the way home I don't get so much as a hiccup from the engine. No CEL either. I don't have a Vagcom either

TIA
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
Likely limp mode due to boost pressure out of spec for a time. That you can get another mile after cycling the key pretty well confirms it.

There is a code set, just not one that an OBDII reader can see - you would need VCDS.

Can you plumb in a boost gauge and determine what boost levels you are seeing?

Alternatively you can get under the car and work the wastegate to see if it is functioning properly. Easiest is with a cheap bicycle foot pump plumbed into the actuator.

Lastly, The N75 (wastegate control valve) is fairly common as they get slow when they age - you can run an actuator test (again with VCDS) or just replace it once you have eliminated everything else.
 

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
1997 B4 Sedan
Also possibly the boost line going into the ECU. Or the boost line inside the ECU. I had the exact same issue a few months ago, even changed the fuel filter and checked inside the tank for debris. Turns out I forgot to plug the boost line back in after working on it.
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Likely limp mode due to boost pressure out of spec for a time. That you can get another mile after cycling the key pretty well confirms it.

There is a code set, just not one that an OBDII reader can see - you would need VCDS.

Can you plumb in a boost gauge and determine what boost levels you are seeing?

Alternatively you can get under the car and work the wastegate to see if it is functioning properly. Easiest is with a cheap bicycle foot pump plumbed into the actuator.

Lastly, The N75 (wastegate control valve) is fairly common as they get slow when they age - you can run an actuator test (again with VCDS) or just replace it once you have eliminated everything else.
Shoot, I wonder if I should just drop it off at a shop, but then again, I'll save money on teh next repair if I just buy the VCDS. Would this one be a good unit (3 car version)? https://store.ross-tech.com/shop/vchv2_ent/

I can try and plump a boost gauge, but I'm not really in a place to spend the money on mych of anything at this point after spending 7k to repair my truck. How hard is the boost line to plumb in?

I'll look into the actuator, hopefully this weekend


Don't you find it odd that the car runs fine in the afternoon though? The issues you talked about seem like it would be a constant issue

Also possibly the boost line going into the ECU. Or the boost line inside the ECU. I had the exact same issue a few months ago, even changed the fuel filter and checked inside the tank for debris. Turns out I forgot to plug the boost line back in after working on it.
Where's that boost line located?


Thanks for your help guys
 

Abacus

That helpful B4 guy
Joined
Nov 10, 2007
Location
Relocated from Maine to Dewey, AZ
TDI
Only the B4V left
Nope, sounds normal to me. It could be condensation in the N75 or a small hole in a boost line. Could be the EGR hanging up as well. I doubt it's anything major and is just an annoyance.

Boost gauges are super simple, just a T off the hose going from the intercom cooler piping to the ECU and then run it into the car.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
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.
Limp mode is triggered by over boosting for a period of time (about 5-10 seconds). This is the most common issue. its usually caused by a bad vac (boost) line to something that causes the waste gate actuator to not work properly when commanded.
Common issues and the fix for them.

Vacuum lines or boost lines: Inspect or replace them all. usually 3mm, 4mm and 5mm hoses. dont use cheep ones, get quality silicone or VW braided lines from IDparts.com or where ever. Not sure about your ECU but on MK3's there is a boost line going into the ecu and inside the ecu to the MAP sensor and it needs replacing too, if you have one.

N75 Valve: you should have a slight clicking from it, kinda like a CCV valve. some times you can clean them, they are not very cheep ($75) for an OEM. usually replacing it is best.

MAF: this is the sensor on the intake air duct right after the filter. ONLY CLEAN WITH MAF cleaner. A cold air intake usually is the culprit for killing them. Check out this link to understand why. Disconnect it and if driving conditions do not improve then its bad. (only after you make sure you have no boost leaks and all your lines are perfect shape.) http://forums.tdiclub.com/showthread.php?t=290373

Boost leaks: Check all your pipes after the turbo to and from the intercooler and to the intake manifold. take them apart, and put back together to make sure no cracks etc. inspect the intercooler too. You will see some oil on the pipes. Its normal. Just wire off the parts your connecting with a light amount of brake clean on a rag. DO NOT spray it into or on the pipe. it could cause a temporary runaway. Happend to me lol, i was lucky, kinda.

When you take your intake pipe off the intake manifold, inspect the intake and see how much soot and crud is caked up. This is caused by the CCV (crank Case Vent) it mixes with the EGR (Exhaust Gas Recirculate) and caused crap to build up. A small amount is ok. Recommend a EGR delete and a tune or hack to remove the CEL (Check Engine Light.) This wont cause limp mode unless its Really bad to the point of causing an over boost. the ECU knows the engine to take in enough air and charges the turbo to supply. This is very uncommon but eh its worth a look.

thats about it. Fix and inspect those items. in that order one at a time with test drive in between to make sure you dont jsut thorw parts at it.

Get someone with VCDS and a VAG-COM connector, or you can autozone it with one of the diagnostic computers they lone you, or a amazon Bluetooth OBDII device. Look up the code you are getting. Limp mode usually does not trigger a CEL (check engine light.)
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Wow, thank you for your time and thorough thoughts on fixing my car! I will report back as soon as I have this unit fixed and tell you what fixed it. Now, I'm off to replace the head gaskets on my 2006 Powerstroke!

Do you guys have a vendor you prefer for the EGR delete and tunes? I don't have emission laws where I live :D
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
Rocketchip, TDtuning, and Malone are the big three - all have their fans and would be able to provide a tune for your car. Search each and make a choice.
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Does a tuner increase fuel mileage? I know Powerstrokes, but not much about the TDI's.

I sure don't want to decrease that since that's the biggest reason I own it
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
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.
If you do it right, yes. So if you add power without changing the GPH (gallons per hour) of the fuel consumption than by definition you are burning more of the same fuel that goes into the car. In a TDI you get more power buy burning more of that fuel in each combustion. Now new nozzles are usually more efficient then stock, upping the boost helps too. I have a very less than ideal set up that most and I went from 90hp to 200-215 is HP and was getting 43mpg now I get about 48 with the way I drive, if I stay on the highway. I drove across 450 miles nonstop at 70mph~ behind a truck drafting and got 66mpg. But when I autocross I get about 8mpg including the drive there and home because racecar, scan gauge and logs say I get about 1mpg when I’m at WOT at 11GPH. When I am driving I get about 2.6ghp on the flat
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Well, I think I'll keep it stock for now, with the exception of the EGR delete maybe. My money pit now is my F350 LOL. Moddifying the TDI is also costly after the VAGCOM, injector nozzles, EGR delete and on and on. My wife won't like having two money pits taking my time and our money! The ROI isn't really there
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
I think I figured it out! I just now got a chance to take a look at this thing. I took advice given, and started by taking the intake piping apart. What I think the issue is, is two loose intake to turbo bolts! They were sooo loose, oil was all over from the CCV system (with I plan to ditch). I haven't tested anything to see if this is the fix, but I'm ordering the parts now. EGR delete, CCV mod and intake parts that I need. Thanks for the pointers!
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Before going down the EGR delete path I would verify that your car is exempt from diesel emissions testing. If you go and modify a bunch of things and then have to go in for inspection there's no telling whether it will pass or not.

Steve
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Well, that didn't work. Back to the drawing board

I'm probably not going to do the EGR delete, not because of the emission restrictions (which I don't have) but because I don't want to spend the money and she has been running for 281k with it intact
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
I have not checked that hose yet. From what I gather it's up under the windshield cowl? That's probably the vac hose that runs from the intake tube?
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
I have not checked that hose yet. From what I gather it's up under the windshield cowl? That's probably the vac hose that runs from the intake tube?
You will want to make sure that all of the vacuum/pressure hoses are intact, but no, the one that commonly develops a hole is inside the ECU. you need to remove the ecu from underneath the passenger side of the cowl and take the ECU cover off (4 screws) to get at the hose inside. there are two small clamps holding it in place. The original is black - this one has been replaced in blue - See here:

 

Palka3

Member
Joined
Dec 21, 2017
Location
Jackson GA
TDI
2002 Jetta TDI
If you've been driving the car all this time (281K miles) you may not realize the power has been dropping due to the vacuum lines, N75 valve and MAP sensor wearing out.

2006PSDSD should follow Mongler98's advice. It's through and not so hard or costly to do. You've gotten your money out of the old hoses, N75 valve and MAP sensor if they haven't been replaced. A local parts store wanted to sell me a new turbo for $600+ with no guarantee of fixing my problem, a problem that was not caused by the turbo or actuator. I replaced the N75 valve, hoses and MAP sensor. I now have a car that runs like new.
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
My brother owned the car before me and he replaced all of the vacuum lines including the ECU hose with silicone hose from idparts at around 150k or so. He also replaced the n75 valve. Are the N75 valves very common to replace numerous times? Are the hoses also? I'm working on the list that Mongler gave me, but the internet side tracks my brain at times with things. I have all day Friday to inspect it all and I hope to find a fix this weekend
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
I've never replaced one in 350k. Hosed it out once a while back.

If he replaced it with a cheapo valve it might need replacing again.

Silicone hose should be good for a long time.
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Good to know. The ones I have removed for other work are the silicone hose, so that's good. I guess there could always be a mouse that's hungry and chewed a hole in one though
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
When I check the n75 for the clicking sound, do I need to use a stethoscope to hear it, or is it pretty obvious? I don't hear anythi bff from it at idle, not can I feel is clicking
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
When I check the n75 for the clicking sound, do I need to use a stethoscope to hear it, or is it pretty obvious? I don't hear anythi bff from it at idle, not can I feel is clicking
I've had some that I can hear with the hood open, but also I've had to use a stethoscope on some too. Also have been able to just touch it and be able to feel it clicking.

Steve
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
I'm thinking N75 doesn't cycle at idle since there's no reason to be moving the TC vanes oops, I mean W/G.

N18 does sometimes.

VCDS can cycle it.
 
Last edited:

MTjake

Veteran Member
Joined
Jun 2, 2003
Location
Belgrade, Montana
TDI
3
check for gunk

How much gunk is in your N75 valve and wastegate control line? I think it was Oilhammer that told me I'm likely just getting blowby past the rings~(these tend to wear by ~200k on the 1Z/AHU, along with 3rd cylinder scoring) finds it's way into the N75 and wastegate actuator hose and when enough accumulates, it gets clogged. The problem is worse when it's cold, because the gunk gets more viscous. At 15F it's probably solid. Problem is fixed by cleaning N75 and line (I use electronic parts cleaner) then blow it out with low pressure air. And then exercise and lube the wastegate because it's probably getting sticky from not moving as much.
Good news is it's cheap and easy to see if this is the problem. Bad news-if this is the issue-it will return once the gunk gets back in there and temps drop.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Steve, does it just sit there and click at idle? Mine does absolutely nothing
Mine seems to always be clicking away, even at idle. This would be both cars, the 97 Mk3 and the AHU powered B3V wagon. They both behave the same.

Steve
 

2006PSDSD

Member
Joined
Dec 7, 2017
Location
Colorado
TDI
1998
Thanks again! I'm going to take a look at that line today. While I messed with things friday, I pulled the line from the n75 and blew some air through it to see the wg open. I swear the car had just a little better power in my travels up and down the mountain for errands. I'll have to grab some electronics cleaner today after church. This is the first I've read about any kind of cylinder issues in this car. I was blaming the oil on the ccv which I plan to reroute to keep thing cleaner

My n75 makes no noise at idle, Steve. I wish I had the vcds to cycle it, but I'm not spending that kind of coin.
 
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