High idle revs when "cold"

[SGKent]

If you will be working on a VW bus you HAVE to own a working tach and timing light. Preferably a dwell tach if you still have points.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[AndyC13]

[airschooled]

Harbor Freight dwell meters work well for about six minutes.

Sears sells an Actron brand that’s about $40 and has tach and dwell functions. I like them for entry level work.

Robbie
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Learn how your vintage VW works. And why it doesn't!
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[TomWesty]

[AndyC13]

I'm in the UK, but something like this will do the job right?

https://www.amazon.co.uk/Automotive-Meter-Multimet...tach+dwell

[AndyC13]

Done a few more "tests" this morning.

1) Fifth injector - Removed the plug to this before start up. Took longer to crank over and fire up, and then a few more seconds to get to a reasonable idle. So it appears that this is working as required on start up.

2) AAR hose - For the first 30-45 seconds, it idled reasonably. I clamped the AAR hose and the idle DID drop. Once I removed the clamp, the idle returned to normal.

3) Fifth injector - After about 45 seconds, the idle started to creep up. I removed the fifth injector plug to see if this was continueing to fire unneccessarily. The idle remained high. So it appears the fifth injector is stopping when needed.

4) AAR hose - With the idle high, I clamped the AAR hose once more. This had NO effect on the RPM.


I have to go out in the bus now, for a reasonably long drive, so we shall see how she fairs.

On my return, I will be sitting down with the FI manual and a multimeter and testing the FI electronics side of things.

[SGKent]

try pulling the parking brake with the bus in neutral, and taking your foot off the brake. See if that changes things.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[AndyC13]

[AndyC13]

My only other thought is that I replaced some of the smaller vacuum hoses with silicon hoses a few months back.

For example, the ones like T, Q, R, I and J in this image.

However, I did use the same ID hoses, but in silicon.

Could that cause it?

[AndyC13]

I have found a post I wrote on another forum in May 2018, where I mentioned a slight "popping" on deceleration.

I think popping is an overstatement. I can bearly hear it. It's more like a dull thud. Probably just linked to the reduced back pressure on the Vintage Speed ehaust.

In this post, I was advised to replace the smaller vacuum hoses. I was advised to use 3mm silicon hose which would stretch nicely over the 5mm fittings. I can't find what it is that I bought, but I suspect I did buy 3mm hose.

Is it possible that the 3mm hose is restricting it somehow?

I will probably replace it to 5mm, as that's what it should be.

[AndyC13]

Well, testing the ECU was a failure!

I hate having this '79 CA FI bus. Everything is different!

The usual L-Jet diagnostic manual wasn't of use. The pins appear to be different on a '79 CA bus.

I found another diagram specific for a '79 CA bus, and a different diagnostic guide, but still no luck! Was getting no readings at all on the pin pairings.

https://www.thesamba.com/vw/archives/manuals/afc_f...Manual.pdf

https://www.thesamba.com/vw/gallery/pix/1719886.jpg


I am going to give it a break for a few days whilst I wait to get some 5mm silicon hoses, and report back!

[AndyC13]

5mm vacuum hose came.

Have replaced about 10 pieces of hose, and appears to have made no difference.

What I have noticed, however, is that there appears to be a reasonable amount of suction on the oil filler tube. Is that normal?

The revs also appear to drop a little when the cap is removed.

[AndyC13]

Well, I appear to have found the "temporary solution" to the problem, and in turn, hopefully we can ID the source of the problem, and a permanent fix.

High cold idle is still a proble, but, if I pump on the brake pedal about 5-10 times, it goes down!

The video link shows the problem and solution from start to finish.
https://www.dropbox.com/s/8a85hrggatrjvs3/Video%2018-09-2018%2C%2017%2006%2025.mov?dl=0

Any ideas?
Presumably something to do with the brake servo and associated hoses?

[AndyC13]

I did the “brake booster test”.

Pumped brake pedal with engine off.
Went “hard”.
Started engine.
Pedal went down a little.

So appears brake booster itself is working, right?

[SGKent]

what do you mean by suction on oil hose? Are you talking the hose to the S-boot, or the oil cap? The oil cap has to be on and sealing or air gets sucked in there, thru the crankcase into the S-boot.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[AndyC13]

[AndyC13]

Finally found a spare 5 minutes to look at this!

Gone back to testing the decel valve.

When it is plumbed is as usual, it revs high.
See video.
https://www.dropbox.com/s/jm9mb1li24q9zoe/Video%2010-10-2018%2C%2016%2001%2039.mov?dl=0

However, when I remove the hose and plug the end, the revs return to normal.
https://www.dropbox.com/s/d0mkliyhrlbbcec/Video%2010-10-2018%2C%2016%2002%2051.mov?dl=0

Is this a sign of the decel valve being faulty?

[SGKent]

[Wildthings]

you can take a can of spray lubricant with a straw and use it to spray down beneath the breaker plates to gives the weights a good cleaning and lubrication. Any extra lube will run out the drain holes where you can sob it up. Afterwards, just keeping the felt lubed should be fine.

[AndyC13]