Yes another Hot idle issue

[Cattwooduk]

I've had a long look through the forums trying to find anything that sounds like my problem, and not found anything quite the same that helps.
Most problems seem to be a high idle when warm because of the waxstat valve failing, or a low idle easily solved by the warm idle screw.
My problem is low idle when warm, around 500-600. But I'm sure it's not just a case of adjusting the warm idle screw, because if I'm driving round normaly with the car up to temp, coming to a stop at lights etc and idling it ticks over at bang on 850 or very close to it.
It's when it's left idling for 5 minutes or so when warm that the rpm starts to drop off until it's rumbling around at 500 or so. If I give it a little rev it drops back to 850 for a split second then immediately drops back down to 500 or so.

I read a post with a link Jimi gave to an article about faulty waxstats and did the 'finger over the hole' thing last night. I let it drop to around 500 rpm, and covered the hole, the engine stuttered and died... So I'm assuming it's a dodgy waxstat. But what I don't understand is that after reading the article, from what I understood, the waxstat sticking open and sucking in air caused the rpm to RISE as it was demanding more fuel to meet the extra air? Have I misread or just confused myself somehow?

I thought I had an idea but the more I read different people's problems the more confused I get ops:
I'm wandering which fix to go for; blocking the waxstat hole with a dust cap with a 5mm hole in it, which as far as I understand would just cut the rpm even lower.
Or to adjust the warm idle screw. But as I said, most of the time while driving and coming to a stop it idles correctly, so putting it up a bit may screw up the idle when it is idling where it should?

Sorry if this is yet another dumb repost, but I'm a little lost!

[spudgun]

Lets see if we can help.

Your normal idle speed of 850 rpm or so is being achieved by air from two sources, the normal idle speed screw and some air leaking through the faulty waxstat.
As we are now nearly in our summer under bonnet engine tempertures are on there way up an causing the wax stat to close more succesfully than it normally would and this is why your noticing an overall drop in idle speed.
You have diagnosed a problem with by the fact you have let it idle at 500rpm, put your finger over the hole and its stalled. Its still drawing in air and shouldn't be.
I hope that has helped clear it up a bit.

[jimi]

^^^^ What he said The valve cap fix is just a fudge IMHO, the best cure is to do the Paul Woods manual choke mod or Spudguns variation on it. Have a look in Know your 2, all the info you need is there

[spudgun]

Jimi's right on the valve cap fix. It proves a point but it's not really a long term fix.
I filled mine with seam sealer. Not what Toyota would recommend but it won't fall out thats for sure.

[Cattwooduk]

Ok well I just had a bit of a play about with the idle speed. I let the engine reach it's normal temp and then let it sit until the rpm drops to 500 again, and played with the idle adjuster until it was at about 850-900 where it seems to sit OK now.
I think I understand, though one thing I don't quite get is that if the waxstat is leaking and drawing in air as it seems to be, wouldn't that make the rpm increase? It seems like it should be a fairly simple principle lol. I think I'm missing the point here and confusing myself.
Waxstat closed - lower idle
Waxstat leaking - should increase idle?
blocking the waxstat - engine stalls, so it is leaking... but why is the idle dropping so low? Simple case of adjusting the idle all along?
Going for a spin to see if it has increased the idle at neutral points while driving, like at lights etc.
Maybe I've just breathed in too much tcut and polish today :-?

[jimi]

What has probably happened is that this has been going on for some time and someone has adjusted the warm idle screw right down to compensate for the higher idle caused by the waxstat not closing properly, hence when you block off the port the car stalls because the warm idle is set too low

[Cattwooduk]

That makes sense. As I expected though, when driving and stopping at lights etc, the idle is now around 1250! It's only if I leave it ticking over for about 5 minutes it will drop to around 900 where I set it. So I guess I'll have to just set it to sit around 700 so when it idles at junctions and things it isn't too high. Still seems a bit odd to me though.

[jimi]

Remember that if you have your foot on the brake or certain electrical loads switched on, the idle-up VSV will kick in and that raises the idle by around 200 rpm

[Cattwooduk]

Ah good point, I went for a lil drive at about 11 last night so although I didn't have cd player or anything on, of course... I had lights on! I'll give it another try tomorow during the day and see