Idle falling, stalling

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toyotally
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My tercel:: 1985 Toyota Tercel SR5

Idle falling, stalling

Post by toyotally » Sat Aug 15, 2020 5:18 pm

Hello T4 community! I just bought my first Tercel 4wd (1985 SR5 wagon with a 3A) and I'm stoked! It's joining my fleet alongside my 1988 Toyota pickup 3.slow V6. But of course, new car, new problems.

I could use some help diagnosing the main issue I'm having with the car. I've been pouring over the forum for days, but I can't find anyone with the same problem as me. If there is an appropriate thread, I apologize, and please direct me.

So. One of two things are happening with the idle: either it is running wicked high, between 1500-1800 RPMs, or it is kind of searching/falling up to 1200 or so until it eventually stalls out. Sometimes it just immediately stalls when I come to a stop. When it is running high (which is less often), it doesn't seem to miss at all, but when it is falling, it has a noticeable miss when revving at lower RPMs. Otherwise, the engine accelerates and runs exceptionally well as far as I can tell.

First thing I assumed was a vacuum leak, as I have dealt with that issue on my pickup. So I replaced many of the vacuum hoses, however, none of the ones I pulled off seemed compromised in any way. I also replaced the PCV valve.

I cleaned the carb window and checked the float level which was correct.

Considering that the car may have been sitting for a long time, I filled up with premium gas and I treated the fuel with a can of Sea Foam. I also cleaned the carb with spray Sea Foam. I noted that the idle steadied as the Sea Foam was being sprayed in the carb, although I didn't know what to make of it. I revved it and as expected, a lot of bluish smoke came out of the exhaust for quite some time, but when I let off the accelerator, the idle continued to fall.

I replaced the spark plugs. The plugs seemed newish, but they were very black on the tips. Oil leak maybe? I verified that the wires were routed to the correct plugs.

I replaced the fuel filter. The filter definitely had some contaminants, but nothing too crazy.

The problem persisted. So I got a can of starting fluid and spot sprayed around vacuum lines and seals to see if it would have any affect. I mostly came up with nothing, until I sprayed around the intake manifold nearer to the front, at which point the idle steadied, although maybe still in the high range.

Should I assume that the culprit is a bad intake manifold gasket? That is my best guess at this point, although I would rather not go to the trouble of replacing it if I'm mistaken.

I apologize for the long winded post, but I didn't want to leave out any relevant details. I truly appreciate any suggestions that y'all may have to offer. Thank you in advance!
Last edited by toyotally on Sat Aug 15, 2020 11:49 pm, edited 1 time in total.

toyotally
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My tercel:: 1985 Toyota Tercel SR5

Re: Idle falling, stalling

Post by toyotally » Sat Aug 15, 2020 5:54 pm

Additonal questions. If I do need to replace the manifold gasket, is there a helpful repair guide for that? Also, is there a preferred brand and part number? I'm finding a number of dissimilar looking gaskets online all claiming to fit my vehicle. Lastly, If I'm digging all the way down there, would it be proper to replace anything else? Like maybe my head gasket as well?

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Mark
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My tercel:: 1984 Automatic, 1981 sedan
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Re: Idle falling, stalling

Post by Mark » Sat Aug 15, 2020 10:02 pm

I don't think I've ever had a vacuum leak in a hose. They always seem to be in the diaphragms of all the diaphragm-operated linkages around the carb like the choke breaker, distributor advance, auxiliary acceleration pump, egr modulator, etc, etc... I'd try pulling off the hoses to these components one at a time and plugging the hose with your finger to see if the idle improves.

toyotally
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My tercel:: 1985 Toyota Tercel SR5

Re: Idle falling, stalling

Post by toyotally » Sun Aug 16, 2020 11:46 am

Mark wrote:
Sat Aug 15, 2020 10:02 pm
I don't think I've ever had a vacuum leak in a hose. They always seem to be in the diaphragms of all the diaphragm-operated linkages around the carb like the choke breaker, distributor advance, auxiliary acceleration pump, egr modulator, etc, etc... I'd try pulling off the hoses to these components one at a time and plugging the hose with your finger to see if the idle improves.
Here in the desert, plastic and rubber parts definitely have a tendency to go bad. I was having vacuum issues on my pickup and it was all dry rotted hoses. But ok, yes, you're right, better to rule out a bad EGR and other vacuum related stuff first before I go n pull the whole thing apart. Thanks for not allowing me to get too hasty. And I can just plug both sides of the hoses that go to those components and notice a difference? Or do I need to bypass them?

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Mark
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My tercel:: 1984 Automatic, 1981 sedan
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Re: Idle falling, stalling

Post by Mark » Sun Aug 16, 2020 10:34 pm

I just unplug the hose from the component and plug the end of the hose. You don't have to bypass it. Some diaphragm-operated components only work when the engine is warm like the EGR so if your idle problems also happen when it is cold, those can probably be ruled out. Some operate only when cold like the auxiliary acceleration pump. Some, like the distributor vacuum advance, operate at all temps.

toyotally
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My tercel:: 1985 Toyota Tercel SR5

Re: Idle falling, stalling

Post by toyotally » Mon Aug 17, 2020 12:24 am

I hunted down every vacuum related component under the hood, trying many of them multiple times, and came up with nothing. Later, I decided to try replacing the fuel pump, but I snapped a bolt in the process, so now I'm at a stand still.

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dlb
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Re: Idle falling, stalling

Post by dlb » Mon Aug 17, 2020 8:38 am

For testing diaphragms on vacuum devices, I suck on the hose that is going to the diaphragm. If I can suck air through, the diaphragm is broken and that hose should be plugged until you can replace the device.

I would also double and triple check to confirm that every hose is going to where it is supposed to. This can be difficult to do visually so for the hoses I'm not 100% positive about, I like to unplug both ends and blow into one of them to confirm air is coming out the other end. I've been surprised several times to find I have messed up routing the hoses, even when I had been confident all were correct.

Another thing I would check for is a leaking AAP diaphragm. This supplies extra fuel when the engine is cold but if the diaphragm breaks (which is fairly common) the vacuum hose that runs from the AAP to the intake manifold sucks gasoline any time there is vacuum present in the manifold -- which includes idle, so this could be your problem. If that's the case, just cap the ports on the AAP and intake manifold and order a carb rebuild kit. It comes with an AAP diaphragm.

Try those, I hope one of them helps.

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Re: Idle falling, stalling

Post by xirdneh » Mon Aug 17, 2020 6:27 pm

Make sure the fuel cut solenoid on back passenger side of carb clicks when it is hooked direct to battery. Then make sure it gets continuous juice while engine is running.
Love those Tercell 4x4 wagons but they sure suffer from road noise.

xirdneh
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Re: Idle falling, stalling

Post by xirdneh » Mon Aug 17, 2020 6:29 pm

There is supposed to be a large vac hose coming from bottom of carb on driver side to yellow plastic thing under air filter housing. Make sure that hose is connected to yellow thing or plugged when air housing is removed.
Love those Tercell 4x4 wagons but they sure suffer from road noise.

toyotally
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My tercel:: 1985 Toyota Tercel SR5

Re: Idle falling, stalling

Post by toyotally » Mon Aug 17, 2020 9:40 pm

Thank you all so much! This is all super helpful info. I really appreciate y'all's dedication to this forum. I still need to decide how to best extract this damn snapped fuel pump bolt (first time I've ever done that - how frustrating!), but once I do, I will perform these tests and let you know what I discover.

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: Idle falling, stalling

Post by Petros » Tue Aug 18, 2020 12:12 am

toyotally, welcome to the forum.

check to see if there fuel in the vac line has fuel in it, that runs from the AAP (auxilarly accelration pump, on the front corner of the carb) and the TVSV (device with vac lines on the coolant outlet on the head). it should be dry, if it has fuel it means there is a bad AAP diaphrame, simplest is to just cap off both ends. if it is leaking fuel into the vac line it will make its way into the intake manifold and cause it run very rich, making the spark plugs black. Another simple thing to do is check the intake/exhaust manifold bolts are tight. some are difficult to reach, but with either a box end wrench (14mm) from under, or a socket and extension, tighten them all up. they tend to work loose from the temperature cycling on the intake/exhaust manifold, when loose they can allow a vac leak at the intake gasket. the gasket is metal and should be fine. it if is damaged, it will have to be replaced, but first see if tightening the nuts/bolts on it work. it is a common problem, causes a slight vac leak around the manifold.

do not replace the gasket unless it is damaged, you should hear a bad leak if it is really bad. there is no reason to replace the head gasket, unless it really needs one. it is a much larger job to replace teh head gasket, than just the intake manifold gasket. There is a head gasket replacement guide I wrote up over in the repair guides section of this forum if you need it.

One other simple thing you might check out, there is a fast idle adjustment on the carb, that is only engaged after a cold start. It hold the idle at a higher speed (like 1600 rpms) until it warms up, than it kicks down (after you press on the accelerator pedal) to normal idle speed. go see the FSM to know how to adjust the idle speed correctly, and also to check out the device on the front of the carb that slows the return of the engine speed to idle, if that is out of adjustment, it will also have trouble at idle. I do not recall what it is called, but it is a small vacuum operated device that slows the throttle's return to idle, it prevents it from slamming shut. That would reduced emissions, it just slows that the last 5-10 degress of throttle plate speed right before it closes. if this is out of adjustment, either too high, or two low, it could make it stall out when you let off the throttle. it is a simple adjustment, you can see the way it works on the front side of the trottle shaft on the outside of the carb, you tweak the throttle and watch it as it returns to idle. the device activates and slows the throttles return to idle speed. check the FSM on how to ajust it, it is simple. procedure.

BTW, what you describe does not sound like it is fuel pump or fuel filter related, check these other items out before you spend time on that.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

xirdneh
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Re: Idle falling, stalling

Post by xirdneh » Tue Aug 18, 2020 12:25 am

on that broken bolt. if any of it is sticking out try small vise grips.
if its flush try a sharp centerpunch. gently imbed into bolt near top and and tap to move it in loosening direction. if your lucky it will move.
if its not flush but recessed it might be very difficult to get it out. good luck
Love those Tercell 4x4 wagons but they sure suffer from road noise.

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