Sudden Drop in Fuel Economy, Strange Temperature, Rough Running

[Highwaylizard]

2014 Jetta Sportwagon 6M TDI with 193,499 miles. Daily driver and only vehicle. No codes outside of P2004, P2006, and P2015.


The Symptoms

While waiting in line at the car wash my temperature spiked to 204. Coolant temperatures never go this high unless I’m doing a regen. Temperatures did go back down once I entered the carwash. Perhaps water on the radiator helped bring temperatures back to normal. To be clear the car was not doing a regen.​

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Running cold on highway – temperature as low as 161 but typically now at 172-179. It takes longer than normal for the car to reach these temperatures. Normally the temperature is pegged at 191 degrees. I drive roughly an hour each way to work so the route and driving conditions are the same everyday.​

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Constant regens while driving that only take the coolant temperature to 190-191. Can hear fans running and smell that “special” regen odor.​

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Engine clatter is now very pronounced whereas before the engine was relatively quiet. Very noticeable during acceleration. It's almost a rattle.​

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Poor tank average mileage. Dropped from 42 MPG tank average to 32 MPG tank average over the past two tanks.​

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Overall lack of power. Several times while accelerating the power has kicked in very sharply at 2200 RPM.​

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Violent engine jerking at 1700 RPM (third gear and roughly 30 MPH) especially when hold this speed.​

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Even when holding steady speed on level ground instant MPG is lousy.​

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Rough idle almost as if it is missing.​

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Chatter at idle.​

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Faint smell (possibly of burning oil?) from time to time but not always.​

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No visual evidence of cross-contamination between the oil and coolant. Both fluid levels seem unchanged.​

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Timing belt, water pump and thermostat replaced November of 2022 at 159,522 miles.​

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Extended crank no start followed by very rough idle.

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Possible Causes

Turbo on the way out?​

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Crankshaft position sensor?​

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Thermostat bad?​

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Clogged injector?​

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Really at a loss here as to what could be causing all of this. I am planning to take the airbox tube off that feeds the turbo and see if the spool is loose/damaged/seized so that I can rule that out. I also think I should pull the hoses off the intercooler and make sure there isn't fluid in there.

Any suggestions, observations, or feedback would be most gratefully appreciated.

 

[STDOUBT]

If you got those codes with VCDS, they mean this. I reckon they could account for your symptoms.
P2004

Possible Causes
Vacuum leak
Faulty Intake Manifold Runner Position Sensor1 (G336)
Intake Manifold Runner binding or sticking

P2006

Possible Causes
Vacuum leak
Faulty Vacuum Solenoid (N316)
Faulty Intake Manifold Runner Position Sensor1 (G336)
Intake Manifold Runner binding or sticking

P2015

008213 - Intake Manifold Flap Position Sensor (Bank 1)
               P2015 - 000 - Implausible Signal - MIL ON

Ross-Tech: News

Your car is 11 years old. There's no way the turbo or CPS are going out unless the car was severely abused.
Thermostat could be a partial culprit, but I think the temp spike is its own issue and not overly concerning in and of itself.

 

[GBaugh]

Here are some additional diagnostic ideas/thoughts.
The constant regens set off red flags in my head. An hour of travel should be plenty of time to manage soot load assuming your car is able to get up to sufficient temp for regen and 160 probably is not sufficient for regen. Malfunctioning intake runners would certainly affect engine breathing and the ability of the aftertreatment sys to manage soot load. Restricted DOC catalyst, DPF or SCR catalyst would affect fuel economy, and power. Exh restriction could be resultant damage from intake manifold issue. To gather diagnostic data, I would suggest looking at measurement values for G505 dpf diff psi sensor, G450 scr catalyst exh psi sensor, as well as exh temp sensors. During regen, you should see a slight temp inc across properly functioning DOC (exh gas temp sensor 2, and 3) and then a temp decrease across dpf (exh gas temp sensor 3, 4). Exh gas temp sensor allocation may be different for your car.

Maybe your engine is overcooling because of the constant regens that trigger your cooling fans to be energized all the time. As you already know, it is normal for regens to elevate eng temps but maybe the constantly energized cooling fans are counteracting that temp inc too much. Usually a restricted exh will cause an inc in eng temps.

Do all your heater vents blow hot air? A plugged heater core would indicate gunk in the coolant sys that could inhibit ability of coolant to circulate.
An infra red temp gun would be probably be a valuable tool here. Look for sudden temp drop across radiator fins that would indicate flow restriction. Check heat exhangers, eng oil, trans cooler, charge air cooler for signs of flow restriction.

An overfueling injector would cause increased exh gas temp at exh manifold sensor (exh gas temp sensor 1).

What is your calc soot load measurement value?
ash load?

You can command a svc regen with VCDS and see what effect it has on soot load just to ensure the sys is able to manage soot load.

What is specified and desired fuel rail injection psi when engine jerking is most pronounced? Do they match? If you suspect a high psi fuel issue, you can check low psi fuel supply system for psi and flow.

To test for exh restriction you can temporarily remove lambda sensor at DOC inlet and see if extended cranking problem disappears.
While you have lambda sensor removed, maybe you can stick a bore scope in sensor port to inspect turbine wheel for contact with turbo housing.

In addition to checking charge air pipe and cooler for oil from turbo, you can also check out turbo by monitoring specified/actual charge boost values and turbo vane specified/actual position in VCDS.

A crank position sensor issue could certainly cause extended cranking but I don't think it would have that much affect on fuel economy and if ckp issue was severe enough to cause extended cranking, you would expect it to trigger ckp faults.

Engine clatter: dual mass flywheel failure can cause clatter, on my passat it was most pronouced cold at idle in park. The clatter noise could be heard coming from flywheel houisng area. Not sure if your car is equipped with DMF.

Probably a good idea to check out those intake runners first.

 

[turbodieseldyke]

There's no way the turbo or CPS are going out unless the car was severely abused.

DPF regens are very abusive to turbos.

 

[STDOUBT]

DPF regens are very abusive to turbos.

Was unaware of that, but another good reason for deletion!

 

[Highwaylizard]

Here are some additional diagnostic ideas/thoughts.
The constant regens set off red flags in my head. An hour of travel should be plenty of time to manage soot load assuming your car is able to get up to sufficient temp for regen and 160 probably is not sufficient for regen. Malfunctioning intake runners would certainly affect engine breathing and the ability of the aftertreatment sys to manage soot load. Restricted DOC catalyst, DPF or SCR catalyst would affect fuel economy, and power. Exh restriction could be resultant damage from intake manifold issue. To gather diagnostic data, I would suggest looking at measurement values for G505 dpf diff psi sensor, G450 scr catalyst exh psi sensor, as well as exh temp sensors. During regen, you should see a slight temp inc across properly functioning DOC (exh gas temp sensor 2, and 3) and then a temp decrease across dpf (exh gas temp sensor 3, 4). Exh gas temp sensor allocation may be different for your car.

Maybe your engine is overcooling because of the constant regens that trigger your cooling fans to be energized all the time. As you already know, it is normal for regens to elevate eng temps but maybe the constantly energized cooling fans are counteracting that temp inc too much. Usually a restricted exh will cause an inc in eng temps.

Do all your heater vents blow hot air? A plugged heater core would indicate gunk in the coolant sys that could inhibit ability of coolant to circulate.
An infra red temp gun would be probably be a valuable tool here. Look for sudden temp drop across radiator fins that would indicate flow restriction. Check heat exhangers, eng oil, trans cooler, charge air cooler for signs of flow restriction.

An overfueling injector would cause increased exh gas temp at exh manifold sensor (exh gas temp sensor 1).

What is your calc soot load measurement value?
ash load?

You can command a svc regen with VCDS and see what effect it has on soot load just to ensure the sys is able to manage soot load.

What is specified and desired fuel rail injection psi when engine jerking is most pronounced? Do they match? If you suspect a high psi fuel issue, you can check low psi fuel supply system for psi and flow.

To test for exh restriction you can temporarily remove lambda sensor at DOC inlet and see if extended cranking problem disappears.
While you have lambda sensor removed, maybe you can stick a bore scope in sensor port to inspect turbine wheel for contact with turbo housing.

In addition to checking charge air pipe and cooler for oil from turbo, you can also check out turbo by monitoring specified/actual charge boost values and turbo vane specified/actual position in VCDS.

A crank position sensor issue could certainly cause extended cranking but I don't think it would have that much affect on fuel economy and if ckp issue was severe enough to cause extended cranking, you would expect it to trigger ckp faults.

Engine clatter: dual mass flywheel failure can cause clatter, on my passat it was most pronouced cold at idle in park. The clatter noise could be heard coming from flywheel houisng area. Not sure if your car is equipped with DMF.

Probably a good idea to check out those intake runners first.

Wow - thank you for the detailed response. A lot to unpack there.

For starters a few additional pieces of information:

I ordered the parts to replace the CPS and thermostat last week and they are scheduled to be delivered tomorrow. I did some investigating and found that the shop I had do the initial work on the car in November of 2022 in fact did not replace the thermostat. I am not a proponent of the parts cannon approach but I do I feel it is a reasonable gamble to replace it as a matter of course. While I am in there I am going to replace the CPS since it will be fairly easy to get to with the thermostat and oil filter housing removed.

I cleaned the intake manifold and the EGR valve last year so I am hoping they are still in decent condition. A few months ago I replaced the motor for the swirl flaps. Additionally I have had the P2015 bracket from Diesel Geek installed for a few years. The P2015, P2004, and P2006 codes are vexing to say the least. I have been told by a few people that the only ways to fix this are either a new intake or to have the swirl flaps tuned out.

My clatter is most pronounced under acceleration even at "warm" operating temperatures. I do not hear it at idle.

My vents all blow hot air.

I have limited resources here in terms of scanning but my handheld Autophix 7610 scanner says:

Soot mass[ml]:210ml​

It is still lower than the​

maximum load of 175.00 ml and does​

not need regeneration.​

Now I'm not very bright but I'm pretty sure the last time I checked 210>175. I would post a picture but for the life of me I cannot figure out how to get a picture to attach here.

Thank you again for your response and suggestions. I will do what I can to get specific answers to the questions and suggestions you made. I really appreciate the feedback.

 

[Highwaylizard]

Well, update . .. .

I replaced the thermostat with a brand-new VW thermostat and o-ring for the hard pipe. Also replaced the crank position sensor, and the gasket and bolts on the oil filter housing. Did an oil change after I got everything back together and a coolant flush. New coolant. Car starts and runs much better now. I had been having long cranks/starts and some serious engine jerking in the 1600 - 2200 RPM range. That has completely cleared up.

Temperature-wise I have a new challenge. Car runs hot according to the Scanguage. Normally (before having the temperature issues described above) the car would run at 191 degrees on the money. Last night I ran 160+ miles on the highway and it ran at 209 degrees the whole way and the fans ran the entire time. The car is not doing a regen. I thought maybe an air dam somewhere in the system? Coolant levels do not change and I do not see any evidence of leaks. I feel like I did a pretty good job of burping the system however I have never done a coolant flush/change/refill on an TDI before and may have overlooked something simple. Heater works great so I do not suspect the heater core is blocked.

I just checked the hoses going to the radiator. Top hose is hot and bottom hose is cool. After running the RPM's up to 2,000 for about 30 seconds the bottom hose is warm but not as hot as the top hose.

Any ideas or insights would be most appreciated.

 

[TurboABA]

Post full, current autoscan.

 

[dannyrew]

Hi I'm new here sorry to.jump.on your thread not sure how to make a new thread, have a 2.0 tdi fr cr170 having issues with overfueling

 

[Highwaylizard]

Turned out to be a faulty thermostat. Apparently rare and unlucky. ID Parts had me make a couple of videos of heating it up in a pot of 200 degree water. Spring did not activate so the valve did not open for the coolant to flow from the radiator to the thermostat. That would explain why the top hose to the radiator was almost too hot to touch and the bottom hose from the radiator to the thermostat was cold.

As an observation it is refreshing to do business with a company that stands behind the products they sell - not many companies do that or are even that eager to help you trouble shoot a product. Absolutely no hesitation in recommending them to anyone. Definitely will continue to do business with them.

Hope this helps someone in the future.

 

[Dannyboy]

CJAA thermostats fail quite often. My son's 2010 has failed open last month and my 2014 is in failure mode ,randomly over-cooling during cold weather.

Definitely not rare.
Just a pain to change.

 

[Highwaylizard]

CJAA thermostats fail quite often. My son's 2010 has failed open last month and my 2014 is in failure mode ,randomly over-cooling during cold weather.

Definitely not rare.
Just a pain to change.

I should have been more accurate in my explanation. This thermostat was defective straight out of the box.

Definitely a hassle to change. I'm actually getting ready to work on mine now as I haven't had time all week.

 

[Dannyboy]

I should have been more accurate in my explanation. This thermostat was defective straight out of the box.

Definitely a hassle to change. I'm actually getting ready to work on mine now as I haven't had time all week.

Having to change the thermostat twice...... ouch

Thanks for the tip,I'll be check mine before installing it for sure, sorry it's at your expense but thanks for letting us know.
Sometimes there's faulty batches out there and if yours is recent buy, chances are the ones I've bought are from that batch

 

[Highwaylizard]

Having to change the thermostat twice...... ouch

Thanks for the tip,I'll be check mine before installing it for sure, sorry it's at your expense but thanks for letting us know.
Sometimes there's faulty batches out there and if yours is recent buy, chances are the ones I've bought are from that batch

With a spinal cord injury to boot - took me a total of nine days to do all this work by myself.

I tested the second thermostat in a pot of water to make sure it was operating correctly before installing it.