4ac randomly cutting out at idle

[Bobomacho]

i'm driving my car on a random day, and i stop at a set of lights just idling quietly. The car will stall out of nowhere.

this is an intermittent problem there is no environmental circumstances at which this event happens.

the carby has been rebuilt in order to cure this but to no avail.

sometimes when i'm warming it up with the autochoke at 2k, it will randomly try to die out but the high idle will catch it.

my leads
--> crap floating around in the carby idle circuit?
anti dieselling solenoid cutting out the system, (it only has one wire so it cannot be reearthed)


anyone else have any ideas?
i'm sure other people have experienced the same thing

[Driftspec]

Yep - mine does exactly the same as you describe. Will idle fine, then suddenly will drop revs and fail. I normally sit with a little throttle percentage to have the revs increased, and to catch it. When it does die and I catch it, it takes a fair bit of throttle + pumping to get it back to idle speed. Also, a lot of black smoke comes up, but I can put that due to oil consumption when it starts stalling.

After living with it for a while now, I have done some investigating, and found a few things:

The carby runs rich, so it isn't a fuel flow issue.
It can do it hot or cold, and even when oil pressure is high and normalised - but it does get worse when the oil is low.
Can do it with high or low fuel loads.
After a stall the secondary throat doesn't always kick in again, I have to wring it out over 5000RPM to 'unstick' it.
It happens most after a long-ish drive at high speeds (when the cruise circuit is mainly being used) - this is the part that has drawn me to the conclusion that it is some sort if intermittent vacuum leak/fault.

There is a lot of perishing rubber piping in and around the carby, so my thoughts is that there is a leak in there, but one that isn't always present. The Toyota mechanical manual seems to agree with it, only if fuel flow is good. Actually finding the leak is another story, but seeing as mine doesn't happen that often (touch wood) I'm not overly concerned - although having said that it got better after topping the oil, making the mixture a little richer and upping the idle speed. But if it happens for you all the time, maybe get a mechanic to look at it, and see if they can fix it for you.

[Hen is a total nutcase]

On Toymods I think River posted one possible reason for this. Some cold idle diaphragm getting old and cracking and leaking. He went into detail about how to fix etc...

A search should bring it up. Though it may even have been in the old forums.

Hen

[dori_86]

yeah i get the same can be at the lights sitting at idle then drop to 500 for a bit then go back to normal... on a good day on a bad day it will conk out, but i have checked points spacing and reset them to normal and have shifted/ moved and have to be reset again?

[Driftspec]

<div class='quotetop'>QUOTE (Hen is a total nutcase @ Feb 24 2008, 10:06 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=491936)</div>
On Toymods I think River posted one possible reason for this. Some cold idle diaphragm getting old and cracking and leaking. He went into detail about how to fix etc...

A search should bring it up. Though it may even have been in the old forums.

Hen[/b]

Now that makes a lot of sense - thanks heaps, I'll see if I can look into this a little more.

Bearing in mind that its a 25 year old car and engine, something like this isn't exactly unexpected