Throttle valve wear in 2.1 WBX

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Mr Bean
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Throttle valve wear in 2.1 WBX

Post by Mr Bean »

After working my way through all (?) of the possible causes of uneven/random speed idling – largely in the area of air leakage/idle control system, I have arrived at the wear in the shaft/butterfly. In the absence of a new/refurbished supplier I am aware and capable in terms of skill/wherewithal of the precise engineering required to refurbish my throttle body and am currently seeking a replacement/donor. My ideal plan would be to machine/adapt each end of the aperture to accept suitable sealed bearings and control the longitudinal position of the shaft etc. However as things stand:

While the idle position switch is currently working correctly I have had to adjust the butterfly stop screw so as to prevent butterfly stiction (jerks open) on the one hand, while restricting leakage past the butterfly to a minimum (tick over too fast). I have managed to get the C0 down to circa 3.0 with a half decent tick over at circa 850 but have no headroom should this drift further.
Anyone got any advice/tips in this field?
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maxstu
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Re: Throttle valve wear in 2.1 WBX

Post by maxstu »

I believe Go Westy in USA offer a refurb. Perhaps they could supply parts instead? Would be mighty interested myself if they did.
My camper is suffering from similar issues. Especially sticky throttle and stalling...right pain in an auto.
Wear causes the butterfly to slightly jam and fools idle control etc seems to be the culprit so lve read so far
One can check butterfly for lateral movement or wear by hand. Any movement will cause issues. However a little up and down movement is acceptable apparently.

Good luck with your butterfly rebuild
Stuart
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Mr Bean
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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

Sorry to hear that other/s suffer this irritating problem although to be fair I don't suppose the possibility of his item being in use up to thirty years after manufacture occurred to VW.
As an aside I do find my WBX has what I would call a flyaway throttle. In practice I find that the smallest movement of the foot pedal results in disproportionate increase in engine RPM. True this is not helped by the "stiction" which we both experience. However both of the Bedfraud CF vans I owned were fitted with a snail cam throttle cable pulley which provided an exponential curve to the throttle response. I intend incorporate such a device in my rebuild (upgrade :wink: ).
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Re: Throttle valve wear in 2.1 WBX

Post by itchyfeet »

I have a spare throttle body, 2 in fact ( along with 1.5 spare injections system ) one has worse wear than the other but I don't want to sell them.

I'd like to help and I have a plan that could help both of us.

How about I lend the worst one to you, you refurb it and fit it then referb yours then send mine back?

If it doesn't help we could talk about the loan of other parts to fault find.

PM me if you want to.
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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

Sounds like a sound proposition but I have just acquired one which is has minimal or no bearing wear and passes the daylight test with flying colours. This one I will install and set up over the weekend so the pressure is off re keeping the van on the road while I work on the refurb. So it looks like the rebuild will take place on the one currently in the van. A fairly basic refurbishment would comprise opening and line reaming of the throttle body and fitting phosphor bronze plain bearings providing that the shaft, which does seem to have been hardened, is not worn. (Counter intuitively it is often the harder surface in a bearing which wears more) Making a new shaft and hardening it could be a faff but is doable. This together with some work on the throttle plate and profiling the bushes to the throttle bore would not change the design and could be successful with minimal work. I do expect problems in removing the throttle plate screws which rightly seem to be well locked in and have minuscule Torx style heads.

The loan of parts for substitution testing would be very helpful if the "new" throttle body does not cure the problem so whether or not that is necessary and given that my basic plan comes good, I would be happy to do the mod on one of your TB's as apart from the reaming and a bit of fettling the only parts would be a couple of custom Phosphor bronze bushes.

Incidentally partially stripping the "new" TB has enabled me to work out how the snail cam style exponential cable pulley can be interfaced with the concentric return spring and actuating arm currently fitted. I guess the redundant ball joint gismo is for the auto box or cruise control.
Wiill keep you updated.
Best regards
Ken
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Re: Throttle valve wear in 2.1 WBX

Post by itchyfeet »

Mr Bean wrote:I have just acquired one which is has minimal or no bearing wear and passes the daylight test with flying colours.

Oh whats the daylight test, maybe mine are not so bad after all?
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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

Peering down the Throttle body with a bright light the other side of the (closed) butterfly. There is a photo of this test on here somewhere.
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Re: Throttle valve wear in 2.1 WBX

Post by itchyfeet »

Mr Bean wrote:Peering down the Throttle body with a bright light the other side of the (closed) butterfly. There is a photo of this test on here somewhere.

how does tbhs tell you if the spindle is worn and leaking?
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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

Well in my case the test showed me that The factory set adjustment was holding the valve plate open slightly. Or had it been set or worn the other way, it might have indicated uneven wear in the plate or body allowing air to pass. Or even that the valve plate was sitting high or low for some reason and not fully closing thereby allowing air to pass over or under it. Of course there could be an argument to be made for there to be some end play in the shaft so that it could self centralize vertically - indeed there is a small amount of end play in the apparently sound TB I have just acquired and it does centralize and ccompletelly close . I have read about shimming on one of the American web sites but this might be a red herring. Not sure what is the design intent but my feeling is that the factory set adjustment screw should be set to hold the butterfly just off jamming so as to prevent friction/wear at the point of throttle plate closure while providing an almost hermetic seal. I seem to remember seeing a process for setting and backing off which mentions the thread pitch and may arrive at the same end result.
Regarding the shaft/bearing interface wear:
The daylight test would clearly not indicate this but wear is quite visible on my bad TB when I wiggle the shaft. However I guess the only way to demonstrate leakage at the shaft/body interface would be to block both ends of the TB and introduce air via the tick over speed adjuster aperture and dunk the TB into a container of water. Anything more than a minimal amount of bubbling probably indicating excessive bearing wear.
E D I T:
Of course bearing that all in mind the Idle speed adjuster passes a competitively large volume of air even when screwed fully in. So the throttle valve plate and bearing leakage has to be significant to be troublesome i.e. to run the idle speed adjuster out of range - that is right in - and still not settle the tick over. My feeling is that the surging. random RPM increase and general irregular tick over problems are as much to do with stuff like butterfly stiction, vague positioning of butterfly upon throttle closure and random idle switch activation as to do with air leakage - all difficult to disassociate worn bearings. :(
Anyway I shall install and set up the "new" TB over the weekend and all will be revealed.
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Re: Throttle valve wear in 2.1 WBX

Post by itchyfeet »

oh, best check the other spare and the one on my van.

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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

itchyfeet wrote:oh, best check the other spare and the one on my van.

Image

Yes it is a very striking way of highlighting a gap however, and bearing in mind Mrs Bean’s comment that I over think stuff :roll: :
On both my TB’s there is a fairly large Gap between the big fat idle speed adjustment screw and the flat section of the butterfly when fully bottomed out. I guess this to prevent the butterfly colliding with it and is taken into account on the total list of contributors to the air mass at tick over required to make up the 14.7:1 air/fuel ratio. So ignoring the blaze of light at 16:00 hrs:

In my reckoning and guessing that the injector contribution of fuel is fixed at tick over in cahoots with the switch and the ECU, then the list would (in a perfect world) be just the big fat idle speed adjustment screw ideally set in the middle of it’s mechanical range, and the Idle control valve busily buzzing away in cahoots with the little box of tricks which is in turn in cahoots with the distributor in terms of RPM. The factory set throttle plate (butterfly) adjuster being set (permanently) to closed without jamming the butterfly in the bore of the TB. Corrections invited.

Any air leaked into the plenum from other sources such as leaking vac hoses being compensated for by moving the big fat idle speed adjustment screw towards the flat section on the throttle plate. Until of course it hits the end stop at which times the slack might be taken up by the Idle control valve which in turn may run out of range.

So assuming that in spite of Mrs Bean rolling her eyes :roll: I have over thought that accurately, the question would be would the leakage around the butterfly be sufficient on it’s own to run the system out of head room in terms of fuel/air ratio?
Again any contributions invited.
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Re: Throttle valve wear in 2.1 WBX

Post by 937carrera »

Mr Bean wrote:
Yes it is a very striking way of highlighting a gap however, and bearing in mind Mrs Bean’s comment that I over think stuff :roll: :
<snip>

Again any contributions invited.

Here's a couple of useful downloads for you DJ owners

http://busman.be/_library/_files/pdf%20 ... nj_Ign.pdf

http://www.vanagonauts.com/files/Digijet_FI.pdf

A cursory examination shows that Digifant is a MAF (Mass Air Flow) system, so the ECU dispenses fuel primarily based on the flow of air, as measured by the potentiometer within the airflow unit. It's essentially an electronic version of K-Jetronic

So whether the air flowing into the engine is going solely through the idle bypass screw, or via the screw and by the side of the throttle valve, the mass of air is unchanged and so the fuel requirement will be correct - other things being equal.

Air leaks after the MAF will of course cause mixture problems, most pronounced at idle.

If the plate for the throttle plate is damaged or isn't centred correctly (perhaps including being off centre and therefore exposing a gap when closed) then more air will go via that route and the range of idle speeds available will be higher than standard.

Air entering via the outside of the throttle body via a worn spindle shaft would also be a source of unmetered air - making the mixture lean

Just my brief 5 penneth
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

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Re: Throttle valve wear in 2.1 WBX

Post by Mr Bean »

Thanks for that 937carrera. Defo more informative than the My Bentley's or Haynes manuals in terms of what is supposed to be going on although I have to be careful not to make a career of it (says he looking over his shoulder for Mrs Beam :roll:).
If my "new" TB does do the job I guess should take a break and let my interest in DJ tech fester for a while. :ok
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Re: Throttle valve wear in 2.1 WBX - update

Post by Mr Bean »

I am just waiting for an Idle Control Valve and Controller (kindly offered as loan for substitution testing :) ) to arrive by post. If successful I hope this will enable me to source the appropriate part to solve this problem.

In the meantime I have unearthed the Idle Valve Controller lurking behind the RHS rear light cluster and found the multi way connector spades completely covered in green verdigris and locked solid into the mating harness connector. And the cover loosened but not detachable - probably by a previous owner. I got it apart by using WD40 and wiggling each of the ten or so spade connectors individually with a thin pair of long nosed pliers and after cleaning the connectors, reassembled it and Araldited the cover back on. If anyone is interested it comprises a pair of classic 90’s tech single sided circuit panels linked together with flexible film wire and rammed full of discrete components including the dreaded electrolytic capacitors of dubious life span :( . Wish I’d photographed it now. Needless to say the idle problem remains. I did find a small hole rusted in the floor of the compartment but probably insignificant in light of the air vent above it. I fixed that anyway.

As mentioned previously and in spite of hitherto acceptable idle, I have never actually been able to detect the vibration in the Idle Control Valve but had another go at seeing what I understand is a PWM trace on the feed wires using an oscilloscope? Again I managed to get up a trace on the screen in the form of a square waveform but this was inconclusive in the presence of massive interference probably from the spark plug leads. I got around twelve volts on the screen grid but can anyone tell me what PWM frequency I should expect to find :?:


Interestingly I did start the van up with the Idle Control Valve installed and powered up but with the Idle Valve Controller unplugged. To my surprise the engine started and straight away settled at 500 RPM and again at 850 RPM when I rotated the big fat idle speed adjuster anticlockwise about one turn. However one might be tempted to leave it at that, I would imagine that there might be long term implications like cold weather starting etc. Plus the unarguable logic that VW would not have created the Idle Speed Controller for purely cosmetic purposes.

While one might imagine so, I would be interested to know for sure whether it is the design intent for the AFM potentiometer to have control over the fuel/air mixture while the throttle is closed and the idle position switch activated :?: Page 51 of this manual: http://www.vanagonauts.com/files/Digijet_FI.pdf" onclick="window.open(this.href);return false; is not clear about this while the adjustable air bypass at the AFM would bring this into question for me.
More as and when.
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Re: Throttle valve wear in 2.1 WBX

Post by 937carrera »

Man with an oscilloscope and knows how to use it eh........ wish I had one and the knowledge, it would make it much easier to diagnose electronic faults on various bits of kit I play with, I have an '80's amp I'm trying to fix at the moment, suspected electrolytics, but not necessarily as Nichicon are very good and I have been given some tests to do on other parts of the circuit.

I typed that while the manual was downloading :)

My reading:

The AFM potentiometer (page 53) tells the ECU how much air is flowing into the engine (and from that flow the mass of air). On idle the ECU still needs to know how much air there is, so that it knows how much fuel to mix with it. Many throttle bodies also incorporate an "off" switch which when closed says to the ECU "I'm on idle, cut off fuel for now and then deliver fuel for when needed to maintain that idle running condition", you can see that there is one on the butterfly in the system overview.

When the engine is cold more air / and a richer fuel mix is required to overcome higher friction of a cold engine, the auxiliary air regulator allows extra air to bypass the butterfly (more flow of air into the engine with no throttle which the AFM will see) while the temperature sensors give the ECU the information to allow it to deliver a richer mixture.

You then have some idle electrickery to stabilise the idle by adjusting ignition timing

Does that make sense ?
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

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