1,6TD JX –Sometimes Revs Not Dropping When Easing Off Throttle

[stuzbot]

Here's one that's been niggling at me for a while now:

Ever since I adjusted the timing on my injection pump...

[it was set at 1,6mm of lift when I bought it and the van sounded like a bag of marbles. Now set to 1mm and sounds great]

...I've had this intermittent problem where, sometimes, when I let in the clutch to change gear, or lift my foot off the pedal when stopped at lights, the engine revs don't drop. So that [in the case of being stopped at lights] the engine will be sitting revving at around 1200 or 1300 and I have to lift the clutch pedal a fraction to the biting point, whereupon the revs will drop back and idle normally at 900.

It only seems to happen in 1st or occasionally 2nd gear, when I'm travelling quite slowly and, the rest of the time, the rev counter is rock solid and bang on the 900 mark. Of course, it may be happening at higher speeds too but I just don't notice as the engine is revving quite high then, anyway.

I've checked the obvious, such as making sure neither pedal or throttle cable are sticking anywhere and the throttle lever on the pump itself springs back nice and strongly when I push it forward by hand and release it. So I'm at a bit of a loss as to what else to check now.

As I've said previously on other threads; my pump has undoubtedly been "fiddled about with" by PO as all the adjustment screws are missing their sealing paint and/or tags and [as mentioned above] the timing was off by a ridiculous amount when I bought it. Unfortunately, as this is a turbo diesel and the pump has an LDA on top [I'm still not sure exactly what that does!] there seem to be a lot more possible adjustment points on it than I'm used to from the normally-aspirated diesels I've always owned before.
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1992 VW LT35 2,4D [SOLD]
1993 VW LT35 2,4D [SOLD]
1992 VW T3 1,6TD Syncro [SOLD]
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[?Waldo?]

Post a pic of the cold start side of the pump (block side - a pic looking into the space between pump and block) so I can see if your pump has the later fast-idle linkage.

[stuzbot]

Wilco.

It'll have to be tomorrow though. It's Dark O'clock over here now.
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Click to view image
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1992 VW LT35 2,4D [SOLD]
1993 VW LT35 2,4D [SOLD]
1992 VW T3 1,6TD Syncro [SOLD]
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[?Waldo?]

It is usually simply the accelerator lever stop screw is too far out. On the older pumps that means that the idle is set too high. On the newer pumps, there are two additional screws for low/high idle so you can lower the accelerator lever stop screw (called the 'residual pressure screw") and then raise the idle to where it was previously.

Another potential cause that is more rare is one or more injector that is peeing a stream below break pressure.

[stuzbot]

Whoops! –that "tomorrow" turned into a bit of a spanish "mañana". I kept forgetting to get out there and snap some pics of my injector pump. It didn't help that the weather's been cold, grey and damp for about the past fortnight. Anyway, here she goes –from as many angles as possible:

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*****************************
Click to view image
*****************************
1992 VW LT35 2,4D [SOLD]
1993 VW LT35 2,4D [SOLD]
1992 VW T3 1,6TD Syncro [SOLD]
*****************************

[?Waldo?]

Your pump does not have the cold start fast idle setup. With pumps that do not have the cold start fast idle setup, 99% of the time, hanging revs are caused simply by the idle speed being set too high. What is your engine idle speed?

[stuzbot]

[zuhandenheit]

I think it would be interesting to see what happens if you set the timing back to 1.6. Maybe the timing change is the direct cause, maybe it's incidental -- e.g., something was disturbed in the process of changing timing, and maybe it's a red herring.

[CohPro]

Throttle cable is routed incorrectly and looks to be over adjusted as the levers don't look to be going back to their stops.

[?Waldo?]

Yeah, something is hanging up the cable. You want the routing to be as relaxed as it can be. Try going under that hose rather than over it.

Also, get an anti-vibration clamp over the 4 metal lines or they will work harden and crack from the engine vibrations.

[stuzbot]

[CohPro]

Cable goes over coolant hose not under.
Just disconnect the cable and see if it behaves properly.

[?Waldo?]

[zuhandenheit]

[outcaststudios]

the routing of the throttle cable:

does it always need to travel through the hole in the firewall with the rubber bushing? when i place my replacement diesel throttle cable cable through that way , its too short. i found that if i ran it the way the OP has it run here, i get JUST enough to be ale to clip it without moving the throttle arm. i dont like this configuration becasue now there is diagonal play that couses the movement to be restricted and so you have to push very hard on the peddle to engage. then it revs up super fast becaseu the tension is restricted. so my question is: are there two different length replacements availabel? for US vs. Euro markets? and is thee another area to look for hangups. as far as i can tell ive checked everything front to back. thanks. oh and also if there is a better thread to ask this in let me know i spent about an hour in search trying to find the right one and didnt want to make a thread.
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'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[Zeitgeist 13]

I have a stock diesel accelerator cable in my mTDI van, and I cut out the entire firewall, so the cable just runs freely up to the pump. So long as it's free and not resting on something it shouldn't, I don't see any reason why it can't bypass the firewall and just mount directly to the pump bracket.
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Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
'01 Weekender --> full camper
y u rune klassik?

[outcaststudios]

hmm. that's good to know. i'll have to move it around and find a spot that is better geometry.
_________________
'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[crazyvwvanman]

There are 2 different length diesel throttle cables used in the US (and more in the rest of the world)
81/82 diesels have the engine and tranny mounted in a similar position as aircooled vans did, as far as front to rear position.
In 83 diesels the tranny and engine were moved back a little, to a similar front to rear position as wbx would also share. This happened mostly to allow the new longer 5 speed tranny to fit.
So diesels from 83-on use a cable 35mm longer than 81/82 do.

The longer cable part number is 251 721 555S

(short cable is 251 721 555C)
Tthe above numbers are for 2wd LHD vehicles like the US models.

Mark

[outcaststudios]

let me guess, the earlier cable is shorter by about an inch and some change? to me it looks like the later cable is what i need, if that is the longer of the two, as you said they moved the location of the arm back so that would make sense.

*edit* LOL i didtn see that you say the exact length 35mm above im getting old and yes its about the difference.
_________________
'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[crazyvwvanman]

I used to buy the longer diesel cable from my VW dealer but NLA.
I see BusDepot lists it as special order. $50

https://www.busdepot.com/251721555s

It is a much more common cable in Europe, and available cheaper there.
If you can wait a while, Latvia is a source of T3 stuff at often lower prices.

https://www.ebay.com/itm/Accelerator-Cable-For-VW-...Sw7PFdY6cF

Mark