1985 hiace 3y - missing on idle and flat spot on acceleration

[Pete30nz]

Hi,
Looking at what to do to fix the miss on idle and flat spot on acceleration.

Plugs are quite new, but that's about it. Have had the van 18 months

I don't have a workshop manual for it, some tuneup specs would be good.

[Pete30nz]

Hi,
Have I posted in the wrong place?

Cheers

[Burntboot]

Nope, you're in the right place.

Generally speaking, that sort of problem is not a "van specific" issue, but what we know so far is, the van is new to you and you replaced the plugs.
Without a service history you will need to go through and bring all the maintenance up to date.
Ignition components would be the first place to start (cap, rotor, wires) not saying its the cause, but until you do the inspections, you wont know.

Having a manual for your market would be extremely helpful, any guidance from this side of the pond will be NA specific and we have had a few members from down your way come and start talking about mysterious things like carburetors.

So, more info required to start.

[Pete30nz]

Hi, sorry for the late reply.
I just done the points, cap and rotor, and condenser.
Adjusted the mixture screw on the carb, screwed it all the way in, until it stopped running on, when you turn the key off.

I'm unable to find where the fuel filter sits. I followed the fuel lines, I can see the manual fuel pump.

It still sound like it's missing on idle.

Took it for a drive while the engine was warm and it seemed OK, but could be better I feel.

[Burntboot]

Replacing the fuel filter is a capital idea but has no impact on the issues you are having.
A compromised filter is going to restrict fuel flow all the time, they do not cause intermittent problems.

I don't understand you comment on carb adjusting, did you screw it all the way in or just till it stops dieseling?

Without knowing what the mixture settings should be, the hack way round would be to dial the idle down to where it should be (800?)
Then turn the mixture screw in (clockwise) until it starts to stumble, then counterclockwise till the idle picks up, then dial in the best idle characteristics between the two. Another thing to do is to put you hand over the top of the carb (while its running) and try to choke off the air being sucked in.
If the idle rises when you do this, it has a vacuum leak and if so, it will need correcting before you can set the mixture correctly.
Conversely, it should stall when you screw it all the way in, if it doesn't, it has a vacuum leak and will need to be corrected.

If the engine is (was) dieseling after shutdown its likely idling too fast, or the timing is set too far advanced.
Have you checked ignition timing and verified everything in the distributor is happy (advance weights, vacuum advance...)

Cheers and good luck.

[Pete30nz]

Hi, I havnt checked the timing yet, I'll track down a timing light. And also I'll need to double check the points gap size.
The mixture screw at the moment is screwed all the way in, and the engine is still idling, but not running on like it was. (Dieseling).

I don't know much about the vac advance or the advance weights.

A good way to find vacumm leak is soapy water, While engine running?

Cheers

[Burntboot]

Soapy water would be a very bad idea, we generally prefer to keep water out of the combustion process.

1st things first, if the engine is still running with the mixture screw snug that is your first problem to solve.
Hopefully you only gently seated that screw as making it tight can damage the tip, would also been good if you happened to count the number of turns you screwed it in (so you can put it back to where it should be) but that is all water under the bridge at this point.

Lets start with the easiest things first, is the choke and throttle linkage free?
You will need to have access to the top of the carb to check out the choke plate (butterfly at top of carb throat)

Crack the throttle open by hand and see if that butterfly moves open and closed, easily.
Follow the linkage on the side of the carb down to the throttle shaft and make sure you can engage fast idle /disengage the fast idle circuit and that everything is free.
Report back your findings and we will go from there.

[Pete30nz]

I'll check the other things you mentioned on the weekend.
I had the air intake off the carb the other day, and when I worked the throttle the butterfly did open. Also while putting the throttle down a bit further the second butterfly did open a small amount, I had the engine idling.

Cheers

[Burntboot]

For vacuum leaks its always a visual inspection first, it could be as simple as a hose off somewhere or it could be as difficult as the carb body leaking.

So start with a visual, if that yields no fruit the next step is use a flammable substance while the engine is runny (not soapy water)
I use a propane torch, crack the valve open and run it over any suspect areas, you will know when you find it as the idle will increase, due to the richer mixture.
If using the propane method, make a point of running the tip over everything not just the carb. Look at things like intake manifold gaskets, carb base plate gaskets (carb body gaskets too) all the vacuum devices from dash pots to VSV's (vacuum switching valves), brake booster, carbon canister.....

Its important to make sure the choke isnt complicating your diagnosis, a stuck closed choke can cause all sorts of issues, especially so if someone previously tried to "fix it" without understanding how it works.

On a cold engine, if you blip the throttle (this takes the tension off the linkage) the choke should snap shut (and engage fast idle).
If you gently release the throttle again you should be able to easily articulate the choke flap back and forth with your fingers.
(If it is stiff to move, spray penetrant into the edges of the choke plate where it pivots as well as the linkages on the side)

There are also several devices that work to control the choke, first up is the unloader, small vac diaphragm that pulls the choke slightly open during start up, once the engine is running the choke heater takes over and slowly opens the choke (the heater could be electric or heat activated or both)
The choke is also connected to the throttle linkage so that it can alter the idle speed to suit the parameters of choke position.

Dieseling (running on) is generally caused by one of 2 factors, either the timing is significantly advanced or the idle speed is too high.

Fuel mixture at idle shouldn't have any effect on dieseling.
I suspect the idle speed is excessively high and this could well be complicating your problem.

And just to make sure that we are all on the same page.
The idle mixture screw should at the base of the carb, here in NA they installed tamper proof plugs over them starting in the '70's
So either someone has removed the plug, NZ never banned making adjustments or you aren't adjusting the right screw.
We should probably figure this part out before going further. lol
Pictures are always helpful.

[Pete30nz]

Photos attached

11745117461174711748

[Pete30nz]

Because the history of the engine is unknown, maintenance wise, I should probably do the intake gasket(s)

11749

[Burntboot]

So 5th pic of the air duct attached, is the black stuff sealant or a breach in the seal?

That does appear to be the idle mixture screw, location is correct, I have seen dummy plastic heads covering real screws, as long as the actual screw turns when you adjust the head, all is good.

With the duct installed, use a pair of needle nose pliers to pinch off any hose you can see (while the engine is running) and see if it alters the idle.
(first rule of sorting vacuum leaks, I coulda mentioned that earlier, sorry)

A good cleaning would make things easier to work around and diagnose. (oily grime can make finding vacuum leaks more difficult)

I wouldn't jump to intake gaskets unless the propane test (or similar) condemns it, ratty looking is one thing, failing a leak test is quite another.

Diagnose the problem first and foremost.
If theres some maintenance issues you can take care of while you're in there, awesome, but they should always remain secondary to resolving your issue.

[Burntboot]

And the 4th pic shows the choke (currently fully open) and the secondary.

When you opened the throttle, and the "2nd" flap opened, that was the mechanical linkage forcing it to open as designed and unrelated to the issue at hand.

Its the plate on the left that is the choke mechanism that we are concerned with and how well it operates

It should be wide open (as in the pic) with the engine warm, conversely, it should be closed if the engine is cold.
With the throttle cracked open (unloaded), it should move back and forth with relative ease.

And just to be clear, the choke be wide open on a hot engine and would stay that way EVEN WEHN COLD, until the throttle is blipped and the mechanical linkages are allowed to reset.

Here in the frigid north, the rule of thumb was 2 pumps of the gas pedal to deliver a fuel charge and set the choke/fast idle, to be ready for ignition.

[Pete30nz]

So 5th pic of the air duct attached, is the black stuff sealant or a breach in the seal?

The 5th pic of the air intake I think it wasn't tightened down when taking that photo. I will recheck. At the same time, id wondered weather I needed to replace that seal ?

[Burntboot]

That seal is important but not critical to running.
Its whole purpose is to keep dirt out, your issues are below that point.

[Pete30nz]

If the weather is good tonight, I'll take a video of the carb with the engine running, and the flaps. I can try for vacumm with my hand over the carb also.

[Pete30nz]

Hi there

Cold start up this arvo, left flap was closed over a bit before I started recording.
https://youtube.com/shorts/vZtzXNKq0c4?feature=share

After auto choke is off, rough or miss sounding idle
https://youtube.com/shorts/2VJLtWt7748?feature=share

Choking carb by hand, checking for vacumm?
https://youtube.com/shorts/hOcnm68ahpY?feature=share

[Burntboot]

It would seem I failed to explain the hand over the carb bit, lets try that again.

You are not looking to cut out all the air, your aim is to seriously reduce the air coming in and then monitor what happens to the idle.
If it has a leak, the idle will increase (a little or a lot, depending on the size of the leak)

The carb is metering the fuel based on the amount of air that travels thru it, if air is getting into the engine someplace other than the carb it will cause the mixture to lean out (more air than fuel), by closing your hand over the carb you causing the mixture to artificially richen.
If the hand test shows no change in idle speed (other than to stumble and die) its not a leak.

Then again, is the mixture screw still cranked in? it should be set to where ever "normal" is (factory setting), before testing occurs.

The fact it runs well on fast idle is only proof fast idle works (which is good)
I have seen engines run quite well at 2500rpm, even when missing one cylinder.

Not sure if its my deafness or the wind noise, but I didnt hear anything horrendous in the idle vid.

[Pete30nz]

The mixture screw is still wound all the way in. I'll have to source a workshop manual for the settings possibly.

Yes it's kind of hard to hear the rough or miss idle

[Burntboot]

I would get it running and up to temperature, then shut it down and turn the mixture screw out 1.5 turns and start it back up and note the idle speed.
Its likely to be somewhere between 1.5 - 2.5 turns out. (make adjustments in 1/4 turn increments, waiting a couple of minutes between adjustments, you cant rush)
If it wont run at all then turn the screw back in to where it will run and start searching for vacuum leaks.

If a visual didnt show anything obvious (hoses dangling, fittings with no hose attached, cracked or swollen hoses) then use your needle nose pliers and pinch off hoses, one at a time until the idle changes and its possible (likely?) theres more than one.
If the pliers test doesn't yield fruit, then move onto the propane torch method (please do this outdoors, windows open)
Things that are common problems are the PCV valve, distributor vacuum advance, base plate of the carb
***DONT use propane around the distributor****
Propane and sparking things dont mix well

Once you solve the leaks, it will just be a matter of setting things up where it idles/feels best
I would aim for an idle speed of 750-800, maybe a titch more if its an automatic

[Pete30nz]

Would you clean the pcv valve, or replace?
Am I right in thinking a test for the pcv valve is blowing through it only one way?

I will try those things you just mentioned.
I'm also going to lend a timing light to check it also.

It's a manual 5 speed.

[Burntboot]

Personally, I would buy a new Toyota part and install it
Then I would look at the old one and see if it can be cleaned up for the spares pile

For me PCV valves have been a lot like thermostats, too many problems with the aftermarkets.
When you're trying to solve a problem, it really sucks to introduce a new one without realizing, btdt

Yes it should only flow one way.

[Pete30nz]

Hi

I've set the point, on the rock, at .016
I now have a timing light to check timing, I think I saw some where 8' btdc? Depending on what fuel is it.

Now I pinched a few vacumm lines, and I also took 2 off, fitted them again. The 2 vac lines are from a sensor or sensor sitting screwed into the water temp area. What are they for? When I pulled them off, the fan seemed to speed up, maybe the idle was a little smoother.

I'm finding a photo of the mixture screw, when I do I'll attach it. It has a warn shoulder shiny bit on it. I may have to do a rebuild.

Update: photo added of mixture screw11777

[Burntboot]

That is not a pretty picture

Can't tell from the pic if its just shiny or actually grooved.
You can try cleaning it up, using something along the lines of 4000 wet with a touch of dish soap to help it cut.
Fold the paper between your thumb and forefinger and rotate, trying to keep the turning and pressure as smooth as possible.
Its supposed to be a slow, gentle, smooth, straight taper to the tip.

If you can get a new one, that would be best, but it isn't something thats going to come in an overhaul kit and I suspect would be a dealer item, only
Try cleaning it up first, unless its heavily grooved, you should be able to make it useable, at least to get things diagnosed.

That thing in the cooling system is a vacuum valve that is controlled by coolant temperature, it will be either open or closed when warm.
Which it is depends on what it controls, following the lines to where they terminate should answer that question.
One end will be the vacuum source, the other the device it is supposed to control.

There really should be a vacuum hose diagram somewhere under the hood, having that info would be helpful in identifying who does what.

Given that you're not the first owner, you cant assume that all the hoses are connected correctly.
Sometimes people pull stuff off and stuff it back on not in the right place (that always makes diagnosing problems even MORE fun).
Having that master plan to guide you, is kinda imperative, otherwise its all just guessing and that rarely works out well.

[Burntboot]

Yes, 8 degrees should be close enough for it to run decent.

[Pete30nz]

Hi, had to spend some time on replacing the radiator, also water pump while I was in there.

I went to check the timing, but I didn't spot the timing marks on the crank pully?

I did clean the pcv valve while I was there also.

[Pete30nz]

I've adjusted the timing by ear at the moment. We are away, and we're on the way to our destination. It wasn't running great. But at the moment, the engine is going good after a dizzy adjustment.

Where does the fuel filter sit please?
I've looked near the fuel tank, but havnt seen it.

Followed the fuel lines up front, looked like one went into a cavity under the driver's seat?
This is a petrol van.

[Burntboot]

These never existed in our market so without access to a manual, it's all just guess work.

FI runs on ~ 40 psi, pump is in the tank, filter is near engine (NA spec=starboard side, aft the front axle'ish) and the lines connect with banjo fittings.
If it has an electric fuel pump, it will have a fuse to protect it, so start your search at the fuse panel.
If there isnt a fuse, it isnt electric

Carbs only require 1-3psi and usually have a mechanical fuel pump, usually driven off the back end of the camshaft and the filter could be anywhere between the tank and the pump. Given the low pressure, they are usually plastic (clear/white) and the fuel lines are connected with spring clamps.

Plug your VIN into Toyodiy and you should be able to find the right parts diagram for your chassis, seeing the correct fuel system diagram should make finding it a little easier

Good luck