Idle Oscillation Fixed

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Highlander
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Idle Oscillation Fixed

Post by Highlander »

I haven't been around for awhile due to overwhelming auto repairs and personal stuff. BUT, I finally fixed the idle oscillation (1800-600) problem and subsequent crashing (stall) on the '85 Teal SR5.
Long story-The wife was/is having problems with vapor lock on her '85, fuel filter full -float bowl empty, Anyway I was perusing the '83 manual that I have since I couldn't find the '85 hardcopy, when I did find the '85, I turned to the FU section and noticed that the fuel cutoff solenoid valves are switched between the two versions.
On the '83s the primary fuel cut solenoid has a single wire and the secondary has two wires.
On the '85s the primary fuel cut is a double wire and the secondary is a single wire.
This was something that I'd never realized, so you have to be careful when you rebuild the carb to install the solenoids the same way that they came out, not the way your book might tell you (depending on your year and manual year).
This all started with the car not idling correctly when I purchased it, I've been futzing around with it for a couple of years since I bought it (it wasn't really necessary since we had the other three running well),my eldest is now about off to college for year 2 and needs transportation so we've been brainstorming as I teach her what's what under the hood and what she can do (working on a degree in Mech Eng). The carb was newly rebuilt when I bought it, but it wasn't done right-gaskets in the wrong places, that kind of thing.
Anyway, I replaced all of the vacuum lines first, tried plugging one at a time, no love. I rebuilt the carb a year ago and while doing so found that the solenoid valves were installed wrong per the '85 FSM. When I reassembled it, I reassembled it per the '85 manual (more on that later), Same problem idle oscillates 1800-650 and ultimately dies and won't restart until it sits for a long time. Pissed off, I just let it sit for awhile to think about it.
I tried swapping out the distributor on the advice of a friend who works with Toys, at least it stopped crashing, but still oscillated at idle, tried to get it through emissions -no such luck, but they identified that it was running lean constantly- more food for thought.
THE FIX-
Then the wife's car started vapor locking, so the perusal of the FSMs. Remembering that the solenoids had been in the wrong positions got me thinking once I saw that they are in different positions year to year, So I checked the wiring diagrams in the back, and found that the ECMs have different inputs between the two year models as well (I'm now thinking that the ECMs can't be swapped out either). Eureka, that's it :idea: , the solenoids are miswired and not opening when they need to be! I mapped out the pins into and out of the connectors and sure enough the socket from the carb was miswired (I'll admit to doing that) for the '85 model year. Once I rewired it, the bloody thing purrs like a kitten at 800-850 RPMs at idle. No crashing, no crap. :P
The solenoids are wired the same in the socket regardless of year, as you look at the socket (from the carb itself) the top right (labelled 1 in '85 FSM) is the positive (Black/white or White/black depending on model year) of the two wire solenoid. The pin below it is the ground (Black) for the same solenoid (labelled 3 in the '85 FSM).
The top left is always the heater for the choke (or 2 in '85 FSM), and the one below that is the single wire solenoid wire (Black/white labelled 4 in '85 FSM) The diagram in the FSM in on page FU-18.
My reasoning as to why-
So the reason for the oscillation at idle was that both of the fuel cut solenoids were off (closed due to no power or no ground) so it was running on what it could get from the idle circuit alone, augmented by the TP and AAP as the vacuum dropped and it tried to crash, then the AAP and TP would apply fuel and open the throttle plate respectively raising the idle to 1800 with the additional fuel and air, the fuel would run out, the vacuum would drop and the cycle started over.
This was also why it was running so lean during the emissions test- no fuel through the main circuits.

I don't know if this is the problem with other cars that have this idle oscillation going on , but I'm not sure that anyone else would have picked up on the concomitant problems- The carb initially being assembled wrong for the year, the incorrect wiring, and the ECM not being able to control the solenoids as a result of both of the aforementioned.
This might need to be in another section, but it really isn't a repair instruction so I put it where people would see it. I hope that this helps someone else, its been a long journey to this point, but its solved now for my car. :mrgreen:
'83 SR5-299K, -tRusty!
'85 SR5-265K--GOLD
'85 SR5-285K-- GOLD-New engine!
'85 SR5-238K -- Teal-Killed by a DD
'58 and '62 Austin-Healey Sprites
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ARCHINSTL
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Re: Idle Oscillation Fixed

Post by ARCHINSTL »

A BIG A-HA !
Way to go!
I'm moving this to the Repair Guides Forum.

I wonder if this would have fixed the (apparently unique to me) problem I had with the RPM oscillation from 1800 to 2200 I encountered with both the OE carb and the rebuilt carb?
See the longest thread in the club's history: https://tercel4wd.com/forums/viewtopic.php? ... it=surging

But - that disappeared with the installation of the Weber and subsequent removal of all emission stuff.
Tom M.
T4WD augury?
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: Idle Oscillation Fixed

Post by Petros »

Nice work. On a 30 year old car you can never know for sure what other previous owners or mechanics have done to it, sometimes they will mess with things that do not need to be messed with, and give the next owner nothing but headaches. It does not help that toyota made minor changes to a lot of the systems from one year to the next of the same model. It seems that each year wiring diagrams have changes, and even changes in the color coding. I have also seen connectors type change from one year to the next on the same component.
'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)
Highlander
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Re: Idle Oscillation Fixed

Post by Highlander »

OH, you mean like the turn signal connectors that differ from '83 to '85? :mrgreen:
'83 SR5-299K, -tRusty!
'85 SR5-265K--GOLD
'85 SR5-285K-- GOLD-New engine!
'85 SR5-238K -- Teal-Killed by a DD
'58 and '62 Austin-Healey Sprites
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Petros
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Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Idle Oscillation Fixed

Post by Petros »

Yes, that is one. I have seen two completely different connectors for the rear wiper power cable even within the same model year. Also the wiper motor connector, identical motor and mount, different plug type!!!!
'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)
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irowiki
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Re: Idle Oscillation Fixed

Post by irowiki »

So did you just take the connectors out of the carb plug and switch them around? I think I need to do exactly this!
Former Tercel Enthusiast (not a practical family car anymore but they still have a place in my heart)

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87 Corolla FX16, 105k
94 Jamboree RV (Ford E-350), 90k
95 Camry Wagon, 170k
97 4runner, 275k
Highlander
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Re: Idle Oscillation Fixed

Post by Highlander »

irowiki wrote:So did you just take the connectors out of the carb plug and switch them around? I think I need to do exactly this!
Sorry I'm late to respond to this :oops:
Exactly- I used a paper clip to push the locking tab back and out of the way. I've got the pinouts on paper with wire colors if you need it, let me know which year you need, and I can scan it or something for you.
'83 SR5-299K, -tRusty!
'85 SR5-265K--GOLD
'85 SR5-285K-- GOLD-New engine!
'85 SR5-238K -- Teal-Killed by a DD
'58 and '62 Austin-Healey Sprites
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irowiki
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Re: Idle Oscillation Fixed

Post by irowiki »

This was for my first gen tercel, I had swapped a second gen carb onto her, which worked great except for the pinouts.

Ended up swapping a good first gen carb back on which works great, so I don't need the pinout diagrams quite yet, thank you though!
Former Tercel Enthusiast (not a practical family car anymore but they still have a place in my heart)

Site administrator, if something is broken, PM me!

87 Corolla FX16, 105k
94 Jamboree RV (Ford E-350), 90k
95 Camry Wagon, 170k
97 4runner, 275k
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