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Discussion Starter · #1 ·
Well, as we know, this is probably one of the main topics right now for the 24V engines. I've experienced fluctuating idle now about three times...twice a few days ago and once this evening...after the car was sitting around for about 10-15 minutes while I was in a movie rental store getting a movie. My car never stalled but nevertheless the idle wasn't constant at startup.
After thinking for a while and observing a couple of things this evening, I've come up with a theory and a couple of ways that we may possibly be able to test it out. But let me recap briefly first.
When my wife and I came back from dinner this evening, while she was preparing some warm drinks, I decided to pop the bonnet for a few minutes and be nosy while the car was cooling down.
OBSERVATIONS
Immediately after opening the bonnet, I had some observations:
a) The radiator fans did not after run. Sometimes they do..particularly after a hard run or sitting in traffic or at traffic lights. But not this time.
b) I felt around to see what was really hot. The air intake box, hose, MAF housing, wiring...all of them...were very hot to the touch. And I mean very hot.
c) The coolant after-run system was working as usual.
As we all know, the buzzing sound coming from the engine bay after the engine has been shut down is due to the coolant after-run system.
Which was all great...but then I began to hear this "tttzzz", "tttttttzzzzzz", "ttttzzzz" sound, similar to what you'd hear from an electrical short...buzzy-tapping sound...just as it would sound if you pronounced the words above.
It was intermittent at first and then turned solid for a good couple of minutes, after which it returned to being intermittent and finally seized. The normal buzzing from the coolant after-run system continued for about one more minute before it also shutdown.
It could also very well be just air bubbles causing vibrations inside the tubing or merely a vibrating valve which also sounds like buzzing....who knows...and I don't think it really relates to much. It was funny to also hear when the coolant after-run system turns off, it sounds like some drained or emptied a pipe.
Anyway, on to my theory
POSSIBLE CAUSE FOR STALLING/BOUNCING IDLE
Now, as we know, I'm sure any component placed near the engine or under the bonnet will need to be tolerant to heat. But when I touched that MAF sensor housing, the air intake, the wires and whatnot, I mean it was quite hot. And understandably so as the VR6 engine runs quite hot.
Think about it, you turn the engine off, the engine bay and all the components become heatsoaked for a short period of time. I'll bet the following right after engine shut down (assuming the radiator fans DO NOT turn on):
a) the MAF sensor actually becomes hotter than it would while the car is running and cool air is running across its surface.
b) the coil packs are heat soaked since no fan every turns on...granted, those fans are probably not there to cool components but that airflow will help dissipate hot air out the sides at the very least.
c) What happens when the car sits around for 10 minutes or so? Heat builds up alot under the bonnet. You come back, start the car, the MAF reads a hot reading during startup, the mixer should be too lean at this time, the electronic system attempts to compensate but their is so much it can do. If the initial fluctuating is too great the system electronics diverges, the car stalls.
I think this could be the culprit.
POSSIBLE TESTS AND COMMON FACTORS
We all know that the following is usually the common scenerio:
a) you drive the car, park it for about 10-30 minutes or so, come back, car stalls
b) this happens usually when the car is warm or hot
HOW ABOUT OBSERVING AND TAKING THESE STEPS?
a) Let's see if the fans turn on after you park the car. If not, and you have idle fluctuation, we may have an issue of definite heat soaking. If the fans do kick in, heat soaking may be less relevant but still possible. See if your fans kick in.
b) Cover the MAF housing, connector and cable harness with heat shield or foil. See if that makes any difference at all.
c) After turning off your car, open the bonnet immediately and let it sit for 15-20 minutes like that before you turn it back on. If you consistently see that your car doesn't stall anymore or doesn't fluctuate in idle, we may have something here.
d) This should not matter regardless of outside temperature or humidity...as localized heat is the issue.

Thoughts/Comments?
I myself shall try the heat shielding approach.
Let's see what happens.
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

It could be heat related or it could be due to improper fuel amount being pumped into the engine before it starts up. It could even be both? From all the heat there could be a lot of fuel(?) condensation in the lines. Maybe by pumping more fuel into the lines it could resolve the stalling problem?
Maybe.


[Modified by Pocket Empty, 12:42 PM 1-26-2003]
 

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Discussion Starter · #5 ·
Re: Stalling and Fluctuating Idle Theory (aavwannabe)

quote:[HR][/HR]everyone and their mother with a turbo car suffers from this issue... and they all have the same theory as you.... its nothing new.[HR][/HR]​
NO sh~t that heatsoaking is nothing new. I'm trying to point out what exactly happens to the system and certain components when they get heatsoaked. So far no one has figured out why these cars are stalling...have you?
It'd be nice if you could add to the thread and this conversation rather than ruining it.



[Modified by Integrale, 12:03 PM 1-26-2003]
 

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Discussion Starter · #6 ·
Re: Stalling and Fluctuating Idle Theory (Pocket Empty)

quote:[HR][/HR]It could be heat related or it could be due to improper fuel amount being pumped into the engine before it starts up. It could even be both? From all the heat there could be a lot of fuel(?) condensation in the lines. Maybe by pumping more fuel into the lines it could resolve the stalling problem?
Maybe.

[Modified by Pocket Empty, 12:42 PM 1-26-2003][HR][/HR]​
Pocket,
possibly. It may very well be fuel related at some level. At this point, your theory is as sound as mine. What we need to try and understand is more than what it's from but why it's happening and play out scenerios where "if this fails, this is what would happen" or "if that fails, this would happen because...." I'm trying to get into the really detailed, microscopic level...what happens to mixture, how does the heat affect this component or that..and how does that affect the system...so on and so forth.
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

Well Intergale I'm not sure if its soo much a heatsoaking issue as much as maybe something else. i say this because I got my car in August and have nearly 13k miles on it and i regualry experience the stalling/ bouncing idle problem...probally on about 40-50% of my starts if not more. Anyway, I've noticed that yes it never really happens inthemorning after the car has been sitting overnight but I know there are mnany instances where I might come home or park somewhere for much longer period of time like and hour or three and the car will still do it. for instance, I might drive to my friends dorm at LMU ( about 30miles from my home) when i park i can hear the fans on. The temp outside might be around 50 degrees and I'll conme back to my car around 3 hours later. The engine has had time to cool because the thermometer will nearly be all the way t the side showing the engine is cold. But yet when I turn the key sure enough the idle will start to raise and dip until either i give it a tap on the gas or the car stalls or what not. so I'm think if the engine is somewhat cold and it still does it, perhaps its a fuelingissue granted that this never happens when i first start the car in the morning froma a comletely cold start....but anyway, just thught I'd add
 

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Discussion Starter · #8 ·
Re: Stalling and Fluctuating Idle Theory (omeezy)

I covered a few connectors and their wires with heat shield and foil...we'll see if it does anything at all. I still stand by my theory that it's a component either failing or developing what they call hysterisis.
This is a problem some electrical and electronic components have with performance. As they cycle through environmental conditions or operating conditions, their performance varies differently as they go from off-on or on-off. You'd expect a linear response where in fact you receive a very non-linear response.
My car actually stalled today. I was getting a hair cut for about 20 minutes...I came out, started the car, it stumbled and stalled. Started up second time. I firmly believe it's either a malfunctioning unit (sensor of somekind or even component, i.e. resistor, etc) or a component that is too severely affected by heat...and this is beginning to show up after many life cycles that were not apparent when new.
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

I took a look closer look today. I noticed the heat is creeping back out from the engine altogether. In fact, I am beginning to think if you insulate the airbox altogether, you are going to stop the heat from dissipating into the environment hence making things worst.
Maybe you can keep that in mind if you find that it is getting worst after you wrap it in insulator.
sorry: cant think right nows cause I am half watching philadelphia; again.
 

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Hi all,
I have seen this problem on my car too with less than 5K miles when it started. When I had the 5K service done, they tried to address the problem by replacing the number 5 spark plug. They said it was fouled. A few days later, the problem was back. Last Monday, I had a coilpack failure (just got my car back after a week), and thought that might have been the cause of the problem. But, it doesn't sound like it will resolve the issue.
Also, I did want to mention that mine has done it once in the morning from a cold start. Heat wouldn't have been an issue then. But, mostly it does it when the car is warm.
I also want to ask, how common are the coil pack failures becoming for the VR6? I know that the 1.8T's are having them pop right and left. I would like to know if mine was a fluke, or if the VR6 is having the same sort of coilpack issues.
Best Regards,
Jeff C
 

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Re: Stalling and Fluctuating Idle Theory (jtcaraway)

the coilpack problem for the vr6 is not a fluke, it's definately happenning, but is not quite as widespread as the 1.8t problem.
hopefully the parts will be in abundance if and when the time comes that anyone who has yet to experience this problem gets hit w/ it.
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

as far as i know, this fluctuating idle thing is relaively harmless. everyone with a 24v has experienced it at least once, and the general consesus is that it happens after about 15-30 minutes of turning the car off...getting food, picking up a friend...etc. call me nuts but that sounds heat related...but anyway, as long as it remains as harmless as it is, i dont care/mind the fluctuating idle.
what im curious to find out is if there is in any way a corrilation between these failing coilpacks, and the idle issue. doubt it, but just thinking
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

try removing the weather stripping between the hood and the winsheild. this will alow the heat to escape much easier. It's re attachable as it's just a strip of rubber. I take this ouot in the summer for a cowl effect.
 

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Discussion Starter · #14 ·
Re: Stalling and Fluctuating Idle Theory (meatwad79)

quote:[HR][/HR]as far as i know, this fluctuating idle thing is relaively harmless. everyone with a 24v has experienced it at least once, and the general consesus is that it happens after about 15-30 minutes of turning the car off...getting food, picking up a friend...etc. call me nuts but that sounds heat related...but anyway, as long as it remains as harmless as it is, i dont care/mind the fluctuating idle.
what im curious to find out is if there is in any way a corrilation between these failing coilpacks, and the idle issue. doubt it, but just thinking[HR][/HR]​
I really don't think there is a correlation between the failings of the coilpacks and the idle issue...I really do think it is heat related and the component being affected is also the component sending an erroneous signal to the FI/air management system saying "lean out the mixture...it's too hot."
While it's not necessarily life threatening, it's definitely a safety issue not by itself, but by what predicament you could catch yourself in if your car fails to stay running. Regardless, cars with less than 30000 miles on them should not experience issues like this.
I emailed VW of A yesterday regarding this and they called me back today. I stated the problem..."Take it to the dealer" was the response. The dealers can't figure it out and I stated for them to take alook at the notes and comments other customers are making here on the Vortex..."Your problem could be a different one"...I said whatever...I'll drive the car until you pay for the towing and repair.
 

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Re: Stalling and Fluctuating Idle Theory (Integrale)

quote:[HR][/HR]
NO sh~t that heatsoaking is nothing new. I'm trying to point out what exactly happens to the system and certain components when they get heatsoaked. So far no one has figured out why these cars are stalling...have you?
It'd be nice if you could add to the thread and this conversation rather than ruining it.
[HR][/HR]​
until VW gives us a more verbose logging option that reading data blocks in VAG-COM, noone will figure it out... anything that anyone comes up with will be a guess AT BEST. Unless of course that person works for VW and has a 24v on a test bench with EVERYTHING logged in real time.
 

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Re: Stalling and Fluctuating Idle Theory (bakersfield_gti)

a hood *vent* may help in some cases.... probably more than a scoop. Heat rises and therefore a well placed vent would allow for the heat the escape. Whereas a scoop is just rushing air intot he engine bay where it is warmed up as well.
 

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Re: Stalling and Fluctuating Idle Theory (bakersfield_gti)

quote:[HR][/HR]maybe i could have a custom hood made to work like the cowl hood.[HR][/HR]​
a "cowl" hood would not be the proper hood to use... cowl's are a form of enhancing induction .. what this would be is an inverted scoop.... it would be scooping hot air out of the engine bay... give me a few minutes... ill see if i can find a picture...
 

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Re: Stalling and Fluctuating Idle Theory (aavwannabe)

well what i was thinking the back of the hood raised so hot air can exit better. its not really a cowl hood, its just raised a little so air can exit. see where im getting at?
 
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