Car dies at idle after getting to operating temp

cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
I checked IQ and it was fluctuating between 4-16. The car seems to drive fine until you gradually let off of the pedal and let it approach idle where the engine rpm fluctuates and the IQ fluctuates in the stated range with it. If you let off the pedal altogether while driving, then it dies right away.

It doesn't do this when the car is warming up. Only when the coolant temp gets to operating temperature.

Any suggestions on what the likely cause is?
 

jrsride2002

Well-known member
Joined
Apr 18, 2013
Location
Houston, TX
TDI
'02 Jetta Wagon TDI
Sounds like it's starving for fuel. How old is your injection pump? How many miles with it?

I had something similar with my Chevy gasser. When I replaced the pump, all went well.

Not a solid answer, but an educated guess.
~Junior

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cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
Well, that's a good question and in the back of my mind I was wondering about its age. I've had the car for the last 100K and it's at 342K now, so that's a good possibility. What's the best way to diagnose it?
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
If it fluctuates like that at idle, could be a worn pump. Check the stuff posted, take a hard look, maybe do some tests, to the wiring. No stored codes?
 

cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
The fuel filter is less than 1 year / 10k miles old, but my daughter's been driving the car so there could be some crud in there. However, it doesn't fluctuate until warm and idling, so I'm thinking the filter shouldn't be causing that. I have not checked the pressure relief valve.

There is a glow plug code, but nothing else.
 

jrsride2002

Well-known member
Joined
Apr 18, 2013
Location
Houston, TX
TDI
'02 Jetta Wagon TDI
I wouldn't know the first thing about diagnosing a IP. But for a moment, let's say it only has 50k on it.

What about your air intake? Garbage fuel, and that kind of milage could leave a lot of carbon deposits in your intake. Not saying seafoam, but a thorough intake cleaning would be my 2nd guess... Which is why I'm making it this inquiry...

Not pointing fingers,. But it could be the effects of neglect of maintenance, to major components. Kind of like skipping a 30K/60K/90K service or something.

I've also seen tons of pics, of plugged EGRs. However, I don't know what the would do.

Again, just bouncing some ideas around for you to poke around for.
~Junior

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cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
I took the car to a local independent VW shop and they thought it was the pump. Replaced the pump and the problem persisted (then removed the new pump). They said it must be the ECU, but they don't do ECUs. (BTW: existing ECU is stage 2 rocketchip, 5+ years old, actual age unknown).

I borrowed a highly tuned ECU from a buddy and the car ran without dying, but the idle still fluctuated (** This was after warming the engine up and running for ~10 minutes. With my own ECU I'm sure it would have died). The fact that the idle fluctuated indicates that there's still a problem and for some reason (* more on this next) the tuned ECU made it continue running.

Tonight, I drove the car for 30 minutes with my ECU (stage2). Here's what happened:
- While warming up, the car does not die and the idle is dead on at 908 rpm
- First 5-15 minutes of driving after warm: I must carefully let my foot off the pedal to let it slowly approach 900 rpm. If I take my foot off the pedal from >1500 rpm the rpm will precipitously drop below 900 before it tries to recover, but it will die.
- After 15 minutes at temperature: Even a small reduction in rpm or idling below 1200 will cause the car to die. To keep the car going you have to keep your foot on the pedal.
- If the car dies in motion, then I put it in gear and release the clutch and generally it will restart.
- If the car dies while at rest, then it is hard as heck to get it restarted. Pedal all the way to the floor and long starter engagement, maybe 30+ seconds, will generally restart the car. Car will restart with ease once it cools off.
- During the last 15 minutes of my 30 ride, I lost it 5 times (2 in motion) 3 while nursing the pedal trying to keep it idling while coming to a stop.

So, does any of this make sense? Any suggestions?
 
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cgates30

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Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
I haven't cleaned it in the 5 years I've owned it. I'll look into cleaning it. That would match the starving of fuel idea, but I'm not sure why the idle would get worse as the car warms up unless the gunk expands with temp to choke the intake.

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ScottySK

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Joined
Dec 18, 2012
Location
Beaumont, AB (CA)
TDI
03 Jetta GLS
ECU needs a good signal from the CPS less than 1500 rpm to idle. Getting any codes?

Sounds like an intermittent failure of the CPS (G28). Try letting it idle, then tap the CPS and see if it dies.


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cgates30

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Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
ECU needs a good signal from the CPS less than 1500 rpm to idle. Getting any codes?

Sounds like an intermittent failure of the CPS (G28). Try letting it idle, then tap the CPS and see if it dies.


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No CEL, but I'll check with vagcom tonight. Is there a screen in vagcom to see THE CPS signal?

Taping the CPS is a good practical test. Will do it.

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ScottySK

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Dec 18, 2012
Location
Beaumont, AB (CA)
TDI
03 Jetta GLS
No CEL, but I'll check with vagcom tonight. Is there a screen in vagcom to see THE CPS signal?

Taping the CPS is a good practical test. Will do it.

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RPM signal but it isn’t reactive enough to see momentary loss.

An oscilloscope is the most accurate way.


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cgates30

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Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
ECU needs a good signal from the CPS less than 1500 rpm to idle. Getting any codes?
Sounds like an intermittent failure of the CPS (G28). Try letting it idle, then tap the CPS and see if it dies.
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Tapping the CPS didn't do anything. I've been measuring the resistance across terminals 1 & 2 of the CPS and noticed that when its hot, the resistance goes up. Higher resistance could mean intermittent RPM signal (just guessing?).

When car was warmed up and stalled, the resistance measured 1450 ohms. This morning when it was cool, it measured 1186 ohms and started right away.

Does anyone have measurements across pins 1 & 2 of the G28 CPS sensor? Warm and cold temperatures would be appreciated.


https://drive.google.com/file/d/1KWfH4ws04AciCi9XvgIlUXOh7kf-wEIC/view?usp=sharing
 
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jcrews

Top Post Dawg
Joined
Jul 28, 2007
Location
Round Rock, TX - VCDS
TDI
All gone
Have a look at basic settings 000.2. It should be around 50-60, even cold. That it starts to stumble as it warms up indicates the timing is probably too late.

Is there a change between early/late in basic settings, channel 04?
 

cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
Have a look at basic settings 000.2. It should be around 50-60, even cold. That it starts to stumble as it warms up indicates the timing is probably too late.

Is there a change between early/late in basic settings, channel 04?
When cold, 000.2 is 50-60, but as the engine temp increased, it dropped slightly below 50. However, when it got to full temp it jumped up and fluctuated in the 60s as the engine rpm also fluctuated. I checked group 004 and there is a difference in timing between early and late. Early is 7-8 degrees and late is 3.5-4.5 at all temps while warming up (and at operating temp).

I didn't drive the car during this warm up and after about 5 minutes of idling at operating temp it eventually died.

I noticed that when I went into 000.2 (Dynamic Start of Injection test) the engine rpm would fluctuate at idle. When I changed to a different group the idle would become more smooth.
 

jcrews

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Round Rock, TX - VCDS
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Please provide some more info:


003 mass air flow (should be 280ish)
019 start/stop voltages


Are you sure the engine sync is correct (lock tools used)?


If the injectors were never serviced, I'd pull them and look for poor spray, leakage, etc. These injectors are basic 2 spring Bosch DI units, so a decent diesel injection shop should have a test stand to at least do a basic check. After 350k-ish miles, they'd be seriously worn.
 

cgates30

Well-known member
Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
Please provide some more info:


003 mass air flow (should be 280ish)
019 start/stop voltages


Are you sure the engine sync is correct (lock tools used)?


If the injectors were never serviced, I'd pull them and look for poor spray, leakage, etc. These injectors are basic 2 spring Bosch DI units, so a decent diesel injection shop should have a test stand to at least do a basic check. After 350k-ish miles, they'd be seriously worn.
The mass airflow changes with the start of injection. At early start, mad flow is ~330 mg/str and at late it is 460mg/str. The voltage is 0.66 V and 0. Sometimes I get another set of numbers in the 3rd/4th blocks.

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cgates30

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Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
Oh, I'm not sure when the injectors we're changed, but they are the Bosio 205's.

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cgates30

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Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
The specified sure is 850 and actual is 440. Car is warming up so I'll see what happens at operating temp.

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jcrews

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Round Rock, TX - VCDS
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The specified sure is 850 and actual is 440. Car is warming up so I'll see what happens at operating temp.

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Typical of disabled EGR in a tuned map. 440 is normal for no EGR.


019 should be about 0.68, 4.5V. Sometimes 0 will be present in one or both, cycling the ignition will re-run the self-test. The engine doesn't need to be started.



Please post a CSV log of groups 001,003 from start up to the point it starts running erratically.
 

cgates30

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Joined
Oct 17, 2009
Location
Oregon
TDI
2002 Jetta, 2000 NB
Here's a link to the file. The file started with the engine pretty warm, but I drove it around the block to help it get fully warm.

https://drive.google.com/file/d/1YyRfZmmK6J33JW0-6Jy07NuguP7LUxRZ/view?usp=sharing

You'll be able to see where the idle fluctuates. I went through some cycles of raising the rpm to get it to the point where it stalled.

For group 019, when I cycled the key I got 0.66V and 4.48V
 
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