Rough idle, ECU, emissons systems, 1981 DLX

[ErickC]

Good mornevenoon. Apologies for the wordy post, (and for the fact that I'm a daft fool with only basic mechanic skills at best) but I rarely have the time to be concise:

I have a California-spec 1981 Tercel DLX with 75,000 miles on it that has a series of issues that I think are most likely related. It misfires a lot from idle to 2,000 RPM or so, gets terrible fuel economy, and the O2 sensor light refuses to extinguish. The carburettor was replaced with a rebuilt one two years ago. I have spent hours - days - whatever - searching for vacuum leaks. I have replaced countless vacuum lines, I have put my head everywhere listening for them, I have doused the engine compartment with cans of carb cleaner, I have had mechanics look at it, nothing can be found at all.

The engine also hesitates in a cyclic manner on the road. It will run fine for five seconds, drag for five seconds, and so on.

But I have a hypothesis:

About a year after I bought it, the Sensor light came on. I had a mechanic replace the upstream sensor along with some other planned maintenance (I think I did it with the 60,000 mile list, along with the PCV, timing belt, et c.). This fixed absolutely nothing, there's always a lovely red hue around the gauge cluster when the engine's running. Obviously, something is still wrong. This means there were four possibilities (as I see it):

1.) The upstream sensor was bad (we can eliminate this, because it was replaced)

2.) The downstream sensor is bad (I did not have this replaced because I keep getting told it doesn't matter)

3.) The ECU is bad

4.) There is a bad connection somewhere

I think the root of the problem may actually be the rear sensor. Most of the people I talk to only really have experience with Mustangs and Broncos and blah, blah, blah, and I keep getting told that there is no way that bad O2 sensors on a car that old will cause any problems at all. I think that the bad rear sensor is causing the ECU to tell the carburettor feedback system to piss off. I think that all of the emissions system tests and adjustments I did per the FSM can't and won't do the tiniest bit of good because the ECU isn't doing its job, it can't, it's not getting data. The FSM does not detail replacement of these sensors - do I have to tear the carpet out, or what?

I think the choke is another problem. I have noticed that the fast idle refuses to kick off on its own. The FSM suggests that fast idle will kick off when the heater/rheostat opens the choke fully. I don't think that this part is doing its job (I went through the carburettor adjustments in the FSM last year, and I seem to remember it not heating up). There are two possibilities for this (again, as I see it):

1.) The unit is bad

2.) It is not getting current

I seem to remember testing the components with a multimeter to Toyota specs before the carb went on, and I don't remember seeing anything unusual. So - what do I do if it's #2? If there were a relay, I'd replace it, but there is no such relay or any provision for one on this car. The FSM leaves out pretty much any and every detail that might help with most of the non-mechanical emissions systems, so I'm at kind of a loss. I tend to gravitate towards #2 because the choke never did its job on the old carb, either.

The FSM is also really sketchy about the float level adjustment, which is a nicer way of saying it hangs you out to dry on it. How do I do that? If it requires taking it apart, I think I might as well replace it. I work in the milling industry, days off are unheard of.

The car is a California-spec model, and I suspect the carburettor I had put on is not correct. As I tend to keep parts I can rebuild on hand, I have the original, supposedly, the only problem was a leaky diaphragm (and I think it was on the throttle positioner dashpot). Is there anything I might consider swapping between the two?

Unplugging the vacuum lines to the distributor doesn't seem to effect much of a change in the ignition timing. One of my original theories was that the diaphragm on the vacuum advancer might be bad, since the car also tends to start kind of hard, which I think is a symptom of the base timing being set to the correct timing for an engine with an operating vacuum advance. The obvious test would be to plug these lines and see if there is any change in the way the engine runs. There wasn't. I suspect this could be a compounded problem - the diaphragm could indeed be bad, but there could be another leak so bad that fixing it doesn't make a difference. As I said before - nobody can find any vacuum leaks on this car.

If part of the problem is the TVSV, what other model cars might have a compatible one? I still have access to my old 86 AE82 Corolla. The car has a blown head gasket (and holes in the floor), but its carburettor always did everything correctly and it got 40 miles to the gallon to the day I bad ordered her. It's a parts car for my best friend's 87 AE82 now. Would this unit be suitable?

The cat is toast, there's nothing in there at all. This was probably related to the bad diaphragm, vacuum leak, and unburnt fuel in the exhaust from the original carb. Will a replacement O2 sensor even work in this state?

Tentatively, the order I plan to address these problems is as follows:

1.) Replace the rear O2 sensor (and cat if necessary)

2.) Replace the distributor

3.) Run through the emissions system tests again, replace the carb heater if necessary, et cetera

4.) Double check the bolts holding the carburettor on. Seal gaskets if possible.

5.) Adjust the idle mixture

Oh, yeah, the plugs and wires are new, too.

Should I just say 'to hell with it' and take it to Toyota and have their technicians deal with it? That's not exactly a cheap route to take, but I do want this car to last, it is practically new, after all.

[xirdneh]

i just posted in "Repair Guides" a write up called "High Idle why?"
try the part that removes all vac lines from carb
at least then you might know if its the carb

[Mark]

I had no idea there was an O2 warning light on these cars. None of my 1st and 2nd gen Tercels ever had one.

[Petros]

welcome to the forum,

unless you are talking about a 1991 or 2001 Tercel, there is no down stream O2 sensor on the first gen Terc.

I would not bother taking it to a dealer to get fixed, most likely no body there knows what to do with it, and will make you pay for them learning on it (and not likely find the problem many many hundreds of $ later). You might get lucky and find a mechanic that is about to retire that knows these cars inside and out, but I would not count on it.

behavior sounds like vac leak, it many not be a vac line or even a gasket, but it could be an internal failure of one of the vac operated devices (making it act like a vac leak). you systematically have to temp plug each component in turn (one at a time) and run the car, if if one of them stops the behavior when you take it out of the circuit.

It is also possible that the rebuilt carb has an internal flaw in it, I would not eliminated it as the source of the problem just because it is new, too many new or rebuilt items are junk right out of the box. check it the same as you would if it was suspect. Because it indeed may the cause.

[ErickC]

The sensor light is the uppermost light on the left side of the gauge cluster. The driver's handbook says that if it illuminated, you should "check oxygen sensor." I had the sensor replaced outright.

It appears I was wrong about there being a rear O2 sensor, as it turns out, per Toyota, the device connected to the cat is a "thermosenser." Can we assume that it's not critical to the car's operation?

[ErickC]

i just posted in "Repair Guides" a write up called "High Idle why?"
try the part that removes all vac lines from carb
at least then you might know if its the carb

Different problem, it idles correctly at the nominal 600-ish RPM with the fast idle disengaged.

What it will not do, however, is kick off the fast idle automatically in cold weather when the engine warms up. You have to floor the throttle momentarily to disengage the fast idle, then it idles at the nominal speed, just as you would do if you wished to cancel it early in a car that functions correctly (like my '82). I assumed this was a problem with the choke system.

[irowiki]

Welcome to the forum, I have an 81 Sedan that I saved from the dead and put a lot of emissions stuff back on it. So I've been around the block so to speak. This may be a little wordy as well as I tend to jump around.

Actually, the fast idle kick back is operated by the choke opener.

"After warm up, this system forcibly holds the choke valve open to prevent an over rich mixture and releases the fast idle to the 3rd step to lower the engine RPM"

But that might not function properly if say, your choke is sticking.


There's a few more places to check for vacuum leaks that you might not have thought of. Get a length of vacuum hose, put it over the port of the disphram in question and suck hard. It should be hard to suck, and if you put your tongue over it, it should hold vacuum. If not, there's your leak.

• Choke opener diaphragm (both of them if equipped)
• both throttle position dispharams (1st gen should have two)
• both choke breaker diaphragms
• both diaphragms on the vacuum advance on the distributor (there's an "upper" and a "lower", one will have one port and connected to ported vac on the carb, and one will be connected to manifold vacuum and either have 1 or 2 ports depending, if it has two ports you have to plug one before sucking on it)
• See if the BVSV or the TVSV are cracked. They're on the water outlet.

The replacement O2 sensor could have been bad too. It happens.

Oh wait I read more of your post:

Unplugging the vacuum lines to the distributor doesn't seem to effect much of a change in the ignition timing. One of my original theories was that the diaphragm on the vacuum advancer might be bad

If a diaphragm is bad on something, then that IS a vacuum leak.

The car is a California-spec model, and I suspect the carburettor I had put on is not correct. As I tend to keep parts I can rebuild on hand, I have the original, supposedly, the only problem was a leaky diaphragm (and I think it was on the throttle positioner dashpot). Is there anything I might consider swapping between the two?

I bought a Tercel wagon that had a reman carburetor, and it turned out the carburetor was bad. It ran like crap. Swapped it with another used carburetor and it has been fine. If you tinker with the connector and the fuel cut solenoid, you CAN run a second gen carb on a first gen, but you're better off finding another first gen carb if you want it to be more plug and play.

Actually, maybe it WAS replaced with a second gen carb, that would be a mess if not accounted for. Post some pictures from a few angles of your carb, and your emissions sticker (vacuum diagram), and the old carb.

Tentatively, the order I plan to address these problems is as follows:

1. If the cat is toast, don't you need to replace that to pass emissions?

2. The distributor may be fine. Replace the cap and rotor first. Check that vacuum advance. I can give picture assistance if needed.

3. double check for leaky diaphragms, especially on your choke opener




Toyota might not be able to help you anyway, my local dealer has no mechanics left that understand the carbed engines, for example

[ErickC]

The carburettor looks outwardly identical to the original, I think it's the right generation, but the wrong sub-model. Toyota lists a different carb for the California-spec models. I don't know that they're all that different. They're kind of vague about it. The rebuild of the original carb has been a work-in-progress for the last year or so. With my 7-day-a-week work schedule, everything is difficult! I hope to finish it when I save enough money to quit!

I do want to replace the cat, but I'm at a loss as to where I'm going to find a California-spec one. I don't know if that sensor goes into the cat or just the outer cover (I'll have to inspect it further), but based on the gasket, I suspect the former. Actually, I don't even know what it (the "thermosenser") does!

Yeah, I figured the choke system was the fast idle problem. I suspect either the choke heater is faulty, or it's not getting current. Since the fast idle never worked right on the last one, either, and I remember testing the components with a multimeter, I suspect the latter. I'm not sure how to deal with that one. A stuck choke, I think, could cause a multitude of other problems. Many of them have symptoms like mine!

EDIT: I think I figured out the relay issue. I was looking in a more general manual than my Toyota one, and I think the relay I'm looking for might be a 1980 thing. The Toyota manual shows exactly where the terminals go, to the regulator. Oops!

I still have access to my old '86 Corolla, and I think I'm going to harvest all of the vacuum components, such as the VTVs, since some may very well be bad. With both of my cars in near-continuous use, it's been difficult to take the '81 out for any length of time to diagnose these issues more thoroughly. I'm probably going to buy my brother a beater so I can have my backup car back again!

But yeah... that sensor light drives me nuts! We'll see what I can get done in the coming weeks.

I have to say, though, true to every other '80s Toyota I've ever owned, with all of these problems, she still never fails to start, not even when it's 30 below. The defroster design may be stupid as stupid gets (hey, let's take all that good hot air and direct it at your feet with the defroster on. It'll pick up all the moisture on your shoes and make the problem worse), but I'll be damned if she fails to start. My '86 Corolla was still getting 40 miles to the gallon with a bad head gasket. You just had to refill the coolant every hundred miles!

[Mark]

What does the warning light say? Could it be the high water temperature light?

[ErickC]

It says "Sensor." The handbook says it means the oxygen sensor should be inspected.

[rer233]

Not sure about Cali spec toyotas, but back in the day, alot of european cars had O2 sensor warning lights that came on after a certain # of miles (60k as i recall.) Some could be reset, but as I recall, Mercedes' reset procedure was "remove the bulb." Just a thought...

[ErickC]

If that were the case, it came on at 60,000 miles, and remains unlit in my '82, which has 118,000! Though, the previous owners were very methodical stewards of the car, so it may have been removed, perhaps?

[Mark]

I was reading a Chilton manual for 1970-1983 Tercel/Corolla/Carina/Starlet and it mentioned the Oxygen Sensor and warning light. It didn't specify which model it applied to so maybe it's relevant to all of them with an oxygen sensor. It said that it's on a timer that lights up the warning light every 30,000 miles to let you know to service the sensor. The counter looks like a small relay box and is located under the left side of the dash and is mounted to the brake pedal bracket. To reset it, take the cover off the box and press the reset button. The warning light should go out.

[rer233]

If it's like the old VWs, the speedo cable should run from the tranny to a box and then from the box to the speedo head. Reset button should be somewhere on the box.

[ErickC]

One issue solved, I found some electrical diagrams in a reference manual, and the sensor light is indeed on a mileage switch - and the reason it's so foreign to most of you is that it is very specific to the 1981 California spec model!

Of all the cars I had to fall for, it had to be the redheaded stepchild of the bunch!

I managed to find a photograph I took of the original vacuum diagram from the hood (before the deer was so kind to ask me to replace it). As I have some vacation coming up, I'm going to just redo all of the vacuum lines and test everything as I go. We'll get the old girl into good mechanical shape yet. Then, we'll consider repainting it.