Surging RPM

[tercle]

Hmmm.
I wonder if the liquid fuel I saw in the primary is normal for 35 degree F temperatures.

Here's what I did today:

I hooked the fuel pump directly to a bottle of gas - no change.
Performed AAP tests.

Swapped the original carburetor back on and
swapped in a known-good fuel pump.

I plugged the line from the front of the carburetor to the charcoal canister - no change.

Got it running before dark and made a run to get flashlight batteries.
Performed AAP hot test again with a better flashlight - still tested OK.

[dlb]

reading over this thread, i'm thinking of what you haven't mentioned checking yet. the EGR is still a likely culprit because if the EGR valve is the source, it will leak exhaust fumes back into the intake regardless of whether vacuum is applied to the EGR diaphragm or not. to block the flow of exhaust into the intake, you must disconnect and plug both the metal tube that runs from the exhaust manifold to the EGR, and the threaded port on the EGR which receives the metal tube. i'm not sure but i would also block the bottom port of the EGR vacuum modulator and the EGR port that goes to it. that would completely seal off the EGR valve and stop any potential leaks there. how many times did i say EGR there?

have you done the tests for the complete carb feedback system? i'm not confident that's it but you may as well rule it out.

another possibility is marginal electrical components, since they tend to malfunction once hot. i've had bad spark plug leads that were fine cold and useless hot. i believe distributor coils can have the same hot/cold performance issues when marginal too, but usually bad wires or coils will act up in all RPM and regardless of idling, accelerating, cruising, etc. it's also worth ruling out though.

[tercle]

I cannot do step 2 of the carb feedback EBCV test on pg EC-33, because there is no way to tell if the RPM drops 300 when I can't get a stable idle.
It is jumping all over the place.
It can change speed 2-3 times per second at its worst.

It will idle fairly smooth only when it is first started and completely cold.

Two sets of spark plug leads have been tested with no change.
Two different distributors have been tested with no change.
Today, I swapped in a EGR valve from a car that runs smooth - with no change.

I have to let it cool down to try the cold TVSV test.

The TP thing on page EC-16 is moving almost in sync with the idle fluctuating.
Seems to be reacting to the symptom rather than a cause, because when I disconnect and plug the line, the fluctuating is still there (maybe a little different).

[TURTCEL]

Any chance you have a leak at the intake manifold gasket?

Peace

[dlb]

Any chance you have a leak at the intake manifold gasket?

this is a good suggestion. check all the nuts and bolts. one member had a leak he couldn't track down until he rebuilt his engine and found his intake was cracked:

https://tercel4wd.com/forums/viewtopic.php?f=2& ... 358#p54358

[tercle]

Any chance you have a leak at the intake manifold gasket?

I was wondering about that.
I went through a couple cans of carburetor cleaner trying to locate a leak, but maybe the crack is underneath or something.
The bolts are all tight.
I checked them when I was swapping carbs yesterday.

It's a new manifold gasket (last month) that was torqued like the manual says.

This fluctuating rpm is really wild and random.
The pattern reminds me of a candle flame on a breezy day.

The ohmmeter tests on the EBCV and vacuum switches A and B on EC-34 checked out.


Need to come up with a plan for next weekend.
I do have a wagon with a bad transmission on the street.
I think I have to loosen the exhaust system and remove the carb to pull the manifolds.
Can I pull only the intake manifold? Isn't it all one piece?
I can't find "manifold" in the manual.

Only one or two neighbors acknowledge me anymore.
Oh. well

My old car just has a weber and a pcv valve. This stuff is too complicated for me.

[xirdneh]

in my case it was probably a rare occurance but
i had to switch the solinoids once
i have had tercels with the two wire solinoid on the back of the carb and some with the single wire on the back
on a tercel that i had swapped the engine,i could not get rid of the up/dn idle no matter what i tried
worked on it for months
i tried disableing the "a" switch because it worked on another tercel but not this one
then one day i was looking at the 83 FSM and noticed the solinoid wire switch was different in one of the pictures
a canada version i believe
also had several old carb re-build kit paper work and some had the solinoids switched
so i tried switching them on this car
i had to cut the wires to do it
and it worked

[TURTCEL]

Be patient with the car tercle...all will work out. There are not a ton of things that can be the reason for you prob but it is just finding out what the problem is that can be frustrating. Nothing is beyond our abilities if we just step back and look at it and say I know I can fix it. The guys on this forum will help you out.

You might consider buying yourself a cheap multimeter and a vacuum guage for doing component testing instead of replacing parts all the time to diangnose an issue, unless it is a super easy swap test. The FSM is pretty descriptive in component testing procedures and the advive from this website will lead you to victory.

I believe you said that you replaced the EGR valve off of another car and it did the same thing. I had a hesitation issue because of a bad EGR valve myself. Istead of just swapping them and thinking that the issue is not the EGR try blocking it off at the vacuum hose that goes to the top of the EGR valve to open it. Do not go through all the other steps of blocking the EGR off yet, but this means of stopping it from opening fully can give you an indication if this valve is bad. The diaphrams on these cars tend to weaken over time an a lot less vacuum is required to open them. It is a test that takes 2 mins. At least try it and let me know what happens.

Next weekend will be your weekend man, I can feel it.

Good luck!

Peace

[TURTCEL]

You can also use an unlit propane torch with a long piece of fuel line on the end of it for locating vacoom leaks. Turn it on to a low flow of propane and while the car is running move the fuel hose around vacuum leak possibilty areas to test for RPM change. It is very hard to get carb cleaner to areas on the bottm side of the intake/exhaust manifold. Just because the top bolts of the maifold are tight I woud find it hard to believe that you were able to check the lower mount bolts with the carb and EGR all in the way. The long hose should be able to get onder the manifold far enough to do some testing.

Another thought is, you said you swapped carbs from another car only to have the same issue occcur. Did you use 3 new carb mounting gaskets when you did this? The carbs look the same but have different imperfections on their mounting surfaces. It is possible thst by reusing old gaskets (dry and crusty) that they might not be sealing well enough and causing a leak. There is a gasket between the intake and the heat sield below the carb that people tend to forget about when cahnging carbs over. I personally had a leak on the bottom gasket which caused runnability issues for me.

The last time did my carb swap I used a different top mounting gasket than the stock large open port gasket. I used a gasket with 2 seperate barrel holes and I noticed that there was no vacuum leak at the base like I kept getting with the stock top gasket design.

Another thing is that there have been a lot of posts of members swapping multiple carbs only to find that the 3rd or 4th carb finally fixed the problem. There is still a possiblity that the carb is an issue. Internal vacuum leaks can form on these carbs and can be almost impossible to diagnose. Over time these carbs become old and worn meaning that even swapping with another older carb might not fix the prob. I had one like this and it drove me nuts. Damn, Terc carbs.

Peace

[tercle]

You might consider buying yourself a cheap multimeter and a vacuum guage for doing component testing instead of replacing parts all the time to diangnose an issue, unless it is a super easy swap test. The FSM is pretty descriptive in component testing procedures and the advive from this website will lead you to victory.

I've got a few cheap multimeters.
It's the only type I usually buy.
I did the tests on the EBCV and vacuum switches with one of them.

And I have a vacuum gauge.

No tachometer, though.

Many of the tests call for a stable rpm to begin with, so I cannot do them.
The fluctuations are too random and rpm is too varied to guess whether rpm dropped or raised when something is tested.

I have a tercel with a bad transmission just sitting there, so after testing as much as I could think of, swapping good components seemed a good way to rule things out.

[TURTCEL]

Awesome that you have a parts car for testing components. That definitely makes swap testing easy. Good luck.

Peace

[tercle]

I like fire and I have been tempted recently...

Would the unlit propane torch cause the idle to stabilize (if it is caused by a vacuum leak and the propane finds it)?

[TURTCEL]

It will cause a change in the idle. Depending on where the leak is located it can either make the idle stabilize or make the car run rough or even die.

Propane is used because it is less harsh on rubber compounds in the system, carb cleaner can actually damage seals by drying them out.

The torch needs to be set at the lowest flow possible where it is still emitting enough propane to be sucked in to a leak area.

I just don't recommend smoking while doing this job...haha.

Peace

[T4WDOR]

I am currently having similar problems after i did an engine swap on my tercel,upon starting the car it surges high and bogs down and continues to surge and bogs sporadically, the throttle is very responsive, maybe a bit too much. Like it may getting too much gas. I know the carb ran on the engine before, which was a california 3ac(i swapped in a 3a-scv) After the swap i connected everything, filled it with all the fluids, new spark plugs and wires. And it turned right over, i was super excited.
But the vacuum lines all look fine, and i put fresh gas and a new fuel filter in it and it still surges and dies like crazy. I'm not sure if i need to adjust the carb or what. But i feel like there is no vac leaks, which i will check soon. I also checked the AAP to no avail. I am incredibly anxious to get it running smooth. I know 3a-scv ran in the car i pulled it out of.
It sounds dumb since i just did an engine swap, but carburetors seem a bit out of my league haha. The only adjustment i know how to make is the idle adjustment. Float levels and all that confuse me. Could it be just a simple carb adjustment?
The only other things i can think of is timing, distributor, EGR valve. Any thing else i can try?

[dlb]

don't be intimidated of carbs. ours look especially weird with all the numerous vac lines but just use a diagram like this one

https://tercel4wd.com/forums/viewtopic.php?f=7&t=2810

and trace all the vac lines to make sure they're properly connected. then check the float level by parking the car on level ground, removing the air filter housing, and looking at the site glass at the front of the carb. the level in the float bowl should be between the two points on the site glass. if it's not, you may need to replace the float or needle valve.

also check the timing. make sure to disconnect and plug the vac advance hoses when setting the timing, and then reconnect them correctly afterward. 5* BTDC is stock timing, 10* BTDC gives better performance though.

with the RPM bouncing around like that, it does sound like either a huge vac leak or an obscenely rich mixture. make sure the brake booster vac hose and the large one that goes to the HIC on the bottom of the air filter are connected, those are two big potential sources of vac leaks.