Idling - particular symptom?

[kervinmervin]

Good evening all,

I was hoping for some help diagnosing an issue, I know there's loads of threads on idling problems but wondering if this is a particular symptom?

Over the past couple of weeks the vans been struggling to idle when stopped, and cuts out or runs really rough. Its always struggled from cold, will start but then I will have to hold revs for a couple of minutes, or increase speed and drive. The starting problem has never really been a issue, but the idling seems to be getting worse....

Anyway, when I disconnect the vacuum tube to the air intake box, the one from the back right of the carb (when facing) it seems to correct itself and improve the idling speed. Is this an issue with the temperature regulator(valve) in the air box, or does it suggest that air is not being drawn in by another part of the carb correctly? Should the temperature regulator allow air to pass quite freely, as there seems to be a lot of resistance.

I've checked and changed the basics, air filter, fuel filter, fuel pump, vacuum pipes, leads, plugs and stared at it quite a bit.

Any thoughts would be appreciated. The van is a 1984 DG, with a standard 2e3 carb.

[kevtherev]

does your choke mechanism function correctly?

taking off the vacuum tube allows air into the mixture so the revs will rise.
this could be an indication of a rich mixture.

the choke flap should be almost shut (3mm gap) at tickover when cold, 5 mins later it should be open fully.

shut



open

[kervinmervin]

Thanks Kev, will check tomorrow morning and report back.

[edoh]

"and stared at it quite a bit."
yep!
my preferred way of dealing with repairs
though it doesn't always seem to work!
hope u get it fixed

[kervinmervin]

I checked this morning, the flap was open before I started the engine, it closed when started, then gradually opened fully - had to give some throttle to stop it stalling and this slightly opened and dropped the flap until it was fully open. Does this suggest correct operation?

Thanks for you help.

[kevtherev]

Idealy one should set the choke by depressing the pedal once before cranking the engine.
This also sets the fast idle cam for cold starting.
The fast ildle helps the engine maintain idle speed when initialy started cold. It is a stepped cam that automatically reduces the engine speed as the temperature rises

Your description is of a fully functioning auto choke mechanism. (and choke pull down unit)

So we need to determine when the engine falters or stalls
is it worse from cold or is it worse with a warm engine... or the same at all temps?

It could simply be the idle speed screw needs a turn or two clockwise...

[kervinmervin]

When I first start, its ok running at high revs. Once I nudge the accelerator it drops down to its lower idle speed, this is when it starts to struggle. However, this doesn't generally seem to be an issue as I get through this by keeping foot slightly on pedal to maintain revs then driving off, its fine at speed. Whilst I say this isn't an issue its something i've lived with for three years.

The rough idling seems generally to be an issue hot or cold, but perhaps slightly worse when cool. After a short drive and idling a junction it runs really rough, again keeping a small amount of power to maintain, this has only recently started happening.

I assume that this wouldn't be connected to a possible issue with the cooling system, it was struggling to get up to operating temperature so i replaced the sender, which seems to have resolved it slightly although I think it still might be a bit slow. Thermostat at ready at next coolant change.

Thanks for your help and patience with this!!

[kevtherev]

The fact that your choke is working correctly means any coolant problem is not affecting idle speed.

I was going to suggest adjusting the auto choke housing and turn it an 1/8th clockwise.
but you say that the engine idles roughly at working temp... this means the problem lies with a universal adjustment

So lets be sure there are no issues with air leaking into the system.
Is there any sign of a back fire or popping on the overrun?
does it falter when you accelerate?
other items to check..
Have you removed the idle speed cut off unit and checked that it is opening fully when the ignition is on? (the one that clicks)

I will suggest increasing in idle speed by the screw should these suggestions be fruitless, it reads like your idle speed is just too low .

BTW when you describe rough idle I assume the engine rocks from side to side sounds a bit clonky, but picks up and runs smoothly once the throttle is opened.

[kervinmervin]

So lets be sure there are no issues with air leaking into the system.

One final thing to check is the brake servo hose, I will replace that as its the old braided one.

Is there any sign of a back fire or popping on the overrun?

no

does it falter when you accelerate?

no faltering, apart from a slight hesitation from cold.

Have you removed the idle speed cut off unit and checked that it is opening fully when the ignition is on? (the one that clicks)

I haven't checked this and will do, is it possible to remove to check full operation with carb in situ?

BTW when you describe rough idle I assume the engine rocks from side to side sounds a bit clonky, but picks up and runs smoothly once the throttle is opened.

exactly like that!

I will have a play around with the idle speed screw, I have adjusted slightly but have been reluctant to disturb to far, assuming the problem lies elsewhere as it was running perfectly a few weeks ago.

again really appreciate advice

[kevtherev]

yes the cut off solenoid can be removed in situ

I can understand your reluctance to mess with the screw setting.
Just remember the turns you do screw it in and if this does not solve the problem it can be returned.
the idle speed screw opens the butterfly slightly, allowing air to bleed in.

It may well be the idle air bleed jet, that has some debris partially blocking it, but this will require removal and some cleaning

[kervinmervin]

Just a quick update, checked the idle speed cut off, in situ for clicking and it clicked. Will try and remove properly to check operation fully later in the week.

Failing that I will remove and clean carb, when the van stops being my main runaround in a couple of weeks. Is this a job to be tackled by a relative novice, is the idle bleed jet visible on the image you posted previously or buried in the depths.

I have given the idle speed screw a couple of turns to the right, this has improved the running, but it does seem to be running faster at idle. I assume this is really compensating for the previous issue.

Thanks again.

[kevtherev]

Turning in the screw will open the butterfly, like having your foot on the acc pedal, it may take a while to get it idling away nice and must be done with a warmed up motor.
Transporters idle at around 1000rpm, it might sound high if it has run low for a while.

[Ian Hulley]

Transporters idle at around 1000rpm, it might sound high if it has run low for a while.

800rpm if you have a tachometer.