RPM Cycling Situation & Vacuum Switch Location Query

[www.geloktech.com]

I had this same issue, with my car I don't think it was the same problem perhaps I can help. Mine was simple it was a 10 Amp fuse located under the car next to the clutch pedal. I took one out I'm not sure which one it was to fix another car and it did this weird cycle thing like yours does. You could try it or perhaps you've done this already sounds like you've gone through it pretty extensively.

[ARCHINSTL]

Well, geloktech, you got me on this one...
I looked under and around the clutch cable in the engine bay and found nothing. Nor I could find any fuse around the pedal in the footwell. There is a fusepanel in the driver's kickpanel on the left, but these dealies don't control anything that would seem to relate to a cycling situation. I also looked in the FSM's electrical chart and could find no reference to a fuse near the clutch.
Wo ist es?
Tom M.

[www.geloktech.com]

I had this problem too I was a fuse, try it. Although it sounds more serious than that.
The fuse was a 10 Amp located under the car next to the clutch..

[takza]

3acPower had a similar problem with his Corolla...found that there were two lines to the EGR...vac mod and one from the ECU....ECU line was the problem?

Easy to test by removing the vac line right at the EGR diaphram and plugging it. Probably already done?

[ARCHINSTL]

I saw 3acpower's post on his EGR, but my EGR is working OK (or seems to be), but has the traditional 3 tubes to it: one from the modulator, one to the modulator, and one to the vac steel line (just like your's, takza).
When I was out and under yesterday, I again looked for the fuse in the clutch area of the body shell and where the clutch cable exits the firewall and still found nothing. This car has zero crud and rust, so the underside and the engine bay are pretty clean. I also found no fuse in the area of pedal attachment. If the clutch switch were not working, I could not get the car started.
I will attempt to locate this fuse again when the icy rain ceases.
It is on an SR5, right?
I think the problem is switch "A" and/or its connection to the ECU, as the problem went away when the vac line to "A" was disconnected. Although I think "A" should be connected for assorted other reasons, as mentioned earlier, I have not yet found an extra "A" to replace it.
The kickpanel fuse box has nothing labelled to affect emissions/driveability.
Thanks,
Tom M.

[coltarms]

My terc does this little cycling thing too. Figured out yours yet?

[ARCHINSTL]

Actually - - No...
I wrote the Mothership in CA a few weeks ago, but have as yet to receive an answer. I plan on writing again.
The cycling did stop when I plugged switch "A's" vac line to the carb. Note that when I unplugged the electrical connection, reasoning that this would have the same result - it did not. So, for ? reason, while the vac line must be plugged, the electrical connection must remain.
The car did then pass the emissions test with flying colors.
The recent MPG has been 30+/- a tad (mostly highway driving).
However, once it warms up (and only then), the rpms do not drop in between shifts as far as they should. Mind, the engine does not race, but the rpms stay above idle a bit. This has no real effect on driveability, but it would seem to affect mileage. This manifestation is not present while coldish. It also disappears when "A's" vac line is unplugged, but of course then the cycling returns.
It obviously has something to do with a gizmo that is affected by the water temperature, but so many things are affected by temperature that I am lost.
It seems that the temp has an effect, per the FSM, at the rpms in question as a part of the Evap system, but I have yet to figure out what does what when.
Tom M.

[xirdneh]

[quote="ARCHINSTL"]WARNING - This is verbose, even for me....
OK - as many know, I have been having an apparently unique problem of the engine revving to 2200, and then immediately dropping on its own to 1800 and then again going to 2200, ad infinitum. This occurred at rest, or not.
So - I reasoned that there was a problem with the "A" switch, regardless of


if a rebuild was done to the carb check to make sure the fuel solenoids are not reversed.
the two wire solenoid should be on the drivers side of the carb
the single wire solenoid on the passenger/aft side of carb.
if they are reversed the car will not idle well and will cycle up and down at best.
disconnecting the vac switch will help the car to idle when the solenoids are reversed.
just got over this recently
sure caused a lot of problems

[4wdchico]

archinstl: did you ever get this issue sorted out? My '85 sr5 4wd CA car tercel has the same problem.

xirdneh: I'm not so sure that your tip about the locations of the fuel solenoids is correct. My '84 sr5 4wd CA car tercel has the single wire solenoid on the drivers side (left) and the double wire unit on the rear/ right. Just went out and checked. It looks like it is a is a newly rebuilt carb and it runs perfect, not a hint of the dreaded cycling.

In the AM I will be yanking all kinds of things off the '84 one part at a time and testing to see which one makes the cycling go away. Just for grins I'm going to swap out the ECU first.

Really glad now that I went thru the Ca clean air course (smog tech program) a while back.

[ARCHINSTL]

Frankly, I never did solve it; as noted in my last post, I eliminated the cycling by plugging the "A" line to the carb while leaving the "A" switch electrically attached. The somewhat slight drop (but NOT a drop as low as it should go) in RPMs between shifts is still there - it's not a lot - just a noticeable number/sound.
The solenoids are hooked up correctly, per the AZ site and the FSM (and pix of various used 3AC/4AC carbs on eBay), despite xirdneh's recommendation to reverse them (mine are like yours).

I still think it is related to either the "A" switch and/or the vapor canister, as those two items seem to be the only ones which, per the FSM, are related to the exact RPM levels (1800 and 2200).
> > > Incidentally, the cycling was there with the OE carb and the first reman carb - and the second reman carb (National Carb replaced the first one under warranty when the AAP and pump failed after 1 1/2 years), so I definitely do not think it is carb-related.

The car did pass the MO emissions in 2005 and 2006 - the latter with lower emissions than the former...! As of last year, cars built prior to 1996 no longer have to go through the MO testing, as they are not OBDII equipped (my Goldie thinks OBDII is related to Obi-Wan Kenobi...).

And, despite wasting a bit of gas between shifts, MPG is still 30 +/-. So - I have not gotten around to looking for another "A" switch and/or canister. If you resolve it - please pass on the word. That not many folks have encountered this unique phenomenon seems odd to me; the cycling certainly makes stop-and-go driving a PITA.

Wow - digging into the ECU - I do not recall that anyone else has ventured that far - keep us advised on this one!
Tom M.

> EDIT < See above red edit on RPMs - additionally, I forgot to mention that I never did hear from Momma Toyota in CA in 2006 when I wrote her - kinda was an irritation....

[4wdchico]

What got me thinking about the ECU is that I tested both the FFS EBCV system and the fuel cut solenoid system and they both failed the dynamic tests given in the oh-so-wonderful FSM. But all of their parts pass the individual components tests that the FSM gives and all other tests that I could dream up also. The one part that is most common to both systems is the ECU. So I yanked it from the '85 with the cycling issue and opened it up and I can see no burned or discolored components.

Hope the two different year ECU's are interchangeable. I'll report back in the AM .

[ARCHINSTL]

Well - it should be interesting...frankly, I did not consider the ECU - wholly from ignorance, I must confess.
xirdneh had some thoughts on the ECU earlier in this thread, which you probably noticed.

All of the individual tests and collective tests I performed indicated that everything was working just fine.
Again - when the "A" vac line was attached and the electrical connection was made, the cycling was there;
.........when the "A" vac line was plugged and the switch was capped and NO electrical connection was made,
.........the cycling was there.
SO - - the line had to be plugged and the switch had to be connected electrically.

I did make an edit to my earlier post vis a vis the RPMs between shifts.
Tom M.

[xirdneh]

after rereading all of this i feel the need to tell about how i dread the cycling problem.
i'm maintaining my three tercels along with three others that friends and relatives have.
i say "dread" because i know sooner or later one of those 6 cars are going to start up with that problem again and i know it will not be easy to remedy.
last saturday it hit again.
ended up trying three spare carbs before finding one that worked fairly well.
just fairly well.
in the past i have switched ECU's with no difference.
disconnected vacuum switches (disconnected vac hose) (car runs hot sometimes but idles well)
cleaned carbs
switched locations of fuel solenoids (my '83 FSM shows opposite of carb rebuild kits and have noted that some '87 carbs were opposite of the '83 FSM) this fixed one car

[4wdchico]

Pretty sure that I have got it, thanks Archinstl for putting me on the path. I just pulled the purge hose that runs from the evap. VSV to the carb off at the carb side. Then I capped off the nipple on the carb. Engine runs perfect, even after warming up, not the slightest hint of cycling, and for sure if I reconnect that line with the engine warmed up, it will. When the ECU switches the VSV open (normally closed)the purge line (attached to the purge pipe on illustration EC1123 pg ec10 FSM) to the carbon canister is acting as a large unrestricted vac leak. Pretty sure that a new carbon canister will have a slow metered flow that will not upset the running of the engine.

Tested the EVAP system back to the tank by pulling a slight vac and it holds it just fine. Plugging the tank pipe inlet (see illustration EC1123 pg ec10 FSM) on the canister does not reduce or restrict the flow out the purge pipe at all.

So I guess that I'm in the market for a new carbon canister, looks like a dealer item, tried Napa and AZ w/o any luck.

[ARCHINSTL]

Well -
THANKS for the heads-up!
Now, when it stops raining here (as soon as that guy with the big boat and the procession of animals leaves...), I will try your procedure, and also reconnect the vac line to switch "A" - I presume you left it connected ? ? ? Did you plug the line into the canister (or cap the canister's port)?

I must admit, when I was trying to get Goldie to pass the first test back in '05, while I suspected the canister, I just did not isolate it - dunno why - guess I was fearful she would not pass/dreadful things would happen.

Incidentally, I just checked RockAuto and O'Reilly to no avail on a new canister. I also checked my favorite OE source, Butler Toy in Indy, with no luck as well - however, I did not call them - a number of times its site showed no OE parts, but by calling, the guys there found the items.
HOWEVER - it seems that sometime ago I found the canister (but do not recall where) - AND - it was well over $200 - I did not investigate further....
Maybe it's time to hit the JYs again.

Again - Thanks ! Can't wait to try it!
Tom M.

ADDENDUM: Just for grins - reread this link, particularly the last few posts on page two, re the canister (ignore the earlier sibling squabbling in mid-thread). https://tercel4wd.com/forums/viewtopic.php? ... r&start=15
I had forgotten about it.