Black Top low idle issue

[bigbacon]

So I am having an odd low idle issue on my black top.

so say I start with a cold engine, turn it on, it runs fine, warms up ok and all seem well. So now it is warmed up and I shut it off, if I turn the car back on, it will now idle at like 500 and it isn't happy.

I had clened and tested the ISCV and it passed the tests and I can hear it working because the air flow throgh the filter on it. Now if I unplug the ISCV once the car starts doing this, it idles fine. so is the ISCV faulty or is something else faulty and causing something else down the line, once warmed up, to tell the engine to this?

Timing is 10BTDC when in diagnostic mode, it is more than 10 when running. Plugs are new. Coolant seems to be bled ok, thermostat is also new.

this only happens once it is warmed up and I start it again. it does start right up when warm but then idles to the point it really wants to die and itsn't a happy camper. it does not do this in diagnostic mode either. diagnostic mode it is solid 1000 idle the entire time. If you punch the gas, it revs up and idle does return to being low with the pot slowing it down. It isn't an instant drop.

possible temp sensor issue?

Least for the time being, what is the down side of driving it with the ISCV unplugged?

[jondee86]

... what is the down side of driving it with the ISCV unplugged?

The ISCV has a spring inside the base... you can see it on the LHS of this pic...



The spring is there to return the rotary solenoid inside the ISCV to the center
position in the event of electrical failure. Having the valve half open is a return
to base type thing... better than let the valve stay fully closed (engine won't run)
or fully open (engine idles at 4000rpm). The spring is made from a bi-metallic
material, and is designed to raise the idle if the engine starts to overheat while
the ISCV is not powered.

So basically, if you are happy to drive the car with the ISCV unplugged (and accept
whatever idle rpm you get) it will not cause any damage to anything else.

Cheers... jondee86

PS: Did you mess with the valve while cleaning it ?

[bigbacon]

i didn't take it apart fully.

i mean it works until the car is warm and something tells the ECU something weird and bam...make it idle low.

[jondee86]

I have never seen any plausible explanation of why a BT would want to idle
as low as 500rpm. There is no legitimate ECU command that would make it
idle that low. So a mystery... and that means it is time to bring these out...

1. Check the ECU for fault codes.
2. Check the TPS is adjusted correctly (IDL switch working).
3. Check the ECU for leaking capacitors.

AFAIK there is a target idle rpm programmed into the ECU. The ECU monitors
the engine rpm and adjusts the ISCV as required to keep the idle rpm on that
target. There will be some corrections for starting, high or low temperature
etc, but nothing that would push the idle down to 500rpm.

Cheers... jondee86

[bigbacon]

no codes

one experiment I did do was to unplug the TPS but no change there. I'll have to test it again. I know I did some of it but don't recall the results. Still one of those things that makes me wonder why it would only happen when hot and not all the time.

[bigbacon]

think I found my miss culprit also.

Cylinder 4, the plug is black/brown all around. 1,2,3 have normal color. didn't seem like oil. it wasnt totally wet or anything. Also looked like the center electrode had a notch in it but I didn't notice if the others had that as well.

Looks more like carbon fouling to me but maybe a combo or both that and oil or fuel..no clue. I just changed all the plug orings a few weeks ago. don't think this is my idle issue but obviously trying to get as much random bits of info about how it is running as I can.

Need those other tune up parts badly i think.

[gotzoom?]

Check to make sure all of the intake ports are open. Both of the blacktops that I rebuilt had completely clogged center intake ports and I needed to use a chisel to get all the carbon out of them.

[bigbacon]

what do you mean by center intake ports? the center ITB buttyflys?. the engine was rebuild top to bottom like 30k miles ago and inside is clean all around but if they were that crusty I think I'd have issues all the time not just when warm.

[bigbacon]

I'm at a loss at this point. No change with new cap, wires, rotor. Still sounds like it is missing and it still idles bad after warming up.

I noticed today that if the car is just sitting there doing nothing it will idle ok. as soon as I actually move it, say back it out of the garage, it will go nuts and start idling low.

SO wish I hadn't taken this on now...Should have just did the reman 16v.....

it is obviously close but I dont even know where to go from here. I've tested everything I can as per the book.

I mean, I could probably drive it but it sure won't be fun to sit there in N at stops.

[jondee86]

This kind of stuff is easier to do hands on, but fkn difficult to do
over the internet. If it was my car I would be taking a look at the
TPS to see if I could figure out if the ECU was actually getting the
message that the engine is supposed to be idling. Reason.. AFAIK
the ISCV is only active when the car is idling, not when it is driving.

That is to say, the ECU will adjust the fuel and ignition timing to get
a nice stable idle, but ONLY if it gets a signal from the TPS IDL switch
that the throttles are closed. Now this is only my theory But I would
mark the TPS so I can put it back where it is, and loosen the fixing
screws off until I could turn the TPS. Then, with the engine warm
and idling low, I would rotate the TPS forward and back to see if there
was a point at which the idle went from idling low to idling normal.

If it does, turn it back to low idle, then sneak up very carefully to
the switching point. As soon as the idle jumps up, stop turning and
tighten the fixing screws. Might not work, but right now you need to
be doing something to elimate possible causes.

Cheers... jondee86

[bigbacon]

ya know...I kept meaning to do that. thanks for reminding me.

I did do the whole unplug the TPS thing but that didn't change anything.

this is why I ask stuff because people at least throw out ideas.....except I just need to remember to actually try them.

[bigbacon]

Ok I tried this. got it warmed up in diagnostic mode, 800-900 idle, bounced with the engine miss/burp/whatever

took it out of diagnostic mode, idle jumps up to 1100 and then starts to slowly go back down to 600 or so and runs rough as hell wanting to die but it won't let itself die. While it was doing that I started twisting the TPS sensor back and forth. Nothing at all changed no matter where the sensor sat.

[jondee86]

OK... seems like the dynamic TPS test was a FAIL. So now you will have
to do the static test as outlined in this page...



This will check the operation of the IDL switch as well as verify that the
resistance values are within range. You will need a multimeter, feeler gauges
and a bit of patience for this one

Cheers... jondee86

[bigbacon]

dumb question, I remember doing this on my 16v but the 20v book doesn't say but does the engine need to be running when you test and adjust this?

[jondee86]

No, the engine should be off and the plug removed from the TPS.

The basic idea is that the IDL switch should change state just before the
throttles go fully closed. The feeler gauges confirm that with the thin feeler
inserted the switch has definitely closed, and with the thick feeler inserted the
switch is definitely open.

The resistances confirm that all is well with the tracks inside the TPS. You
should get a nice smooth rise/drop in resistance as you rotate the throttles
from closed to open, and be within the stated range.

Cheers... jondee86

[bigbacon]

cool. I'm actually going to pull off the manifold and adjust all the stops first.

do you have pull vacuum on the idle opener as well? it doesn't say that but least on my car rght now, it pushed up and the gap on the stop is actually way larger than the maximum allowed so cana't even do the tests.

[jondee86]

Yes... as the throttle opener does push the throttles off the stops when
the engine is off, you need to tie down the opener or temporarily remove
it to set the stops and TPS. If you are lucky enough to have a Mityvac, you
can also use that to hold the opener in the retracted position.

Cheers... jondee86

[bigbacon]

wow, the process to adjust the stops is quite amazing... what a chore and I really hope I did it right and didn't miss anything.

Went to adjust the TPS and.........My multimeter is broken now... situation normal..

and just in case it isn't my multimeter going nutso...can anyone confirm that toyota part 8945222080 will work on the BT? The is new the part number that replaced 89452-12080 as per Lithiatoyota's website.

[bigbacon]

new multimeter, TPS checks out and is adjusted so that all tests are in spec.

[jondee86]

Seems like the TPS is all good, so the next thing to look at will be
the O2 sensor. The AE111 (20V BT) is notorious for having various
engine issues that trace back to the O2 sensor. This link is just one
of many similar posts on the subject...
http://s15.zetaboards.com/AE111_Forum/topic/6746130/1/

O2 sensors clogged with soot can sometimes be rejuvenated by
giving them a good brushing to clean off the bulk of the soot, and
then heating the sensor with a butane torch to burn off remaining
deposits. There are how-too's on Youtube.

And this needs to considered in conjunction with the "missing" issue
that you have. When a cylinder missfires it will cause the O2 sensor
to report a lean mixture, and the ECU will compensate with more
fuel. So you will need to try and pin this down... try removing plug
leads one at a time, swap injectors around etc., to see if you can
identify one cylinder/injector/plug that is bad.

Cheers... jondee86

[bigbacon]

I am pretty sure it is cylinder #4 as when I pulled the plugs a week or so ago, 1,2, and 3 had a normal color while #4 was black. I am not sure yet if it was because of fuel or oil or both but the car isn't blowing the normal "im burning oil" exhaust.

My O2 sensor was brought over from my 16v. 4 wire version from an NA. I have a second O2 sensor but it has no connecter, i'll have to take a look at this again as it came with the engine. I guess I could get pigtail for it and solder it up and try it. the O2 sensor wiring was messed up when I got it. the O2 sensor was hard wired into it with no connector and was completely removed from the harness. I had to add the connector and fix it back to the harness. the sensor that came with it was a Denso 5540

My 02 sensor is attached to the manifold. I hope that isn't part of the problem. Doesn't the ECU throw codes for O2 sensor junk tohugh?

Yoshi is also sending me out another 20v ECU just to test with since mine has that suspected bad looking repair or overclock or whatever someone did to it. I have a syncrometer on the way as well to do the throttle balancing.

[jondee86]

Good move !! I hadn't picked up that you had a dodgy ECU, and that would
have been my next suggestion... trying another ECU. The 20V has something
of a reputation for ECU problems due to faulty capacitors etc., and when
random weird stuff starts happening, it is often the ECU to blame.

Cheers... jondee86

[bigbacon]

I did replace one capacitor on mine but yea, someone else had a go at in the past and it honestly looks like a bad repair job with solder all over the place.

[bigbacon]

Adjusting the TPS and the throttle stops seems to have made a little bit of a difference in the lumpy sound but not the idle issue. I went to test the timing again and the idle is so low can't really even do it as the marks are jumping all over the place as it tries to keep itself alive.

Going to have to test the O2 sensor now. I did a little bit but I didn't print out the instructions so I didn't really know what Iwas testing for other than putting the multimeter up to the terminals.

Engine did actually die on me today as well which was the first time it has done that.

other odd thing is that when turning the distibutor, it didn't really seem like it had and affect on anything with the way it was running.

[jondee86]

other odd thing is that when turning the distibutor, it didn't really seem like it
had and affect on anything with the way it was running.

Yes... that is one of the odd things that is happening. When the engine is
not in diagnostic mode, turning the distributor should change the timing,
and changing the timing should change the engine speed.
Now here I can only theorise, as I don't know the answers, but...
1. If the engine speed does not change, perhaps the ECU is adjusting the
ISCV to keep the idle speed on target ? Without a good running 20V to
experiment on, I don't know what can be expected.
2. If the ECU is adjusting the engine idle speed with the ISCV, why does it
not hold the idle speed on target at other times ?
3. In diagnostic mode I would expect the ISCV to be de-activated, but this
is something I cannot confirm,

We know that the ISCV tests good, and that the TPS tests good. It is almost
like at certain times the ECU is not getting a RPM signal from the distributor.
But no rpm signal means the engine does not run. So the only logical conclusion
is that the ISCV is not getting the correct control signals some of the time.

You say that you do get a stable idle at some times, and not at others, which
is in line with this conclusion. So at this stage my guess would be a wiring
fault (intermittent) between the ECU and the ISCV, or a borked ECU. Getting
the loan ECU installed will eliminated one of these possibilities

Cheers... jondee86

[bigbacon]

I have to try the distributor again when the engine is cold to see what happens but it really sounded and felt like nothing much was happening when moving it but the timing did change but I think it was running so rough at that point it really didn't matter what it was doing.

I printed out the BGB page on testing the ECU wiring so I'll run through that. Once I can test with the alternate ECU Yoshi is sending me I will most likely pull the entire harness out and probably send it off to 220v and have him redo the entire thing for me.

I am getting to the point that there really is nothng left to test and/or things I can't actually adjust/test because the car won't idle right.

Yea anymore the idle just seems to do this

start out at 1500, slowly drop as it warms up to about 1000. Once you start messing around with opening the throttle (either by hand or by driving it) it gets wacky once the car is completely warmed up. it can go to 800 and bounce betwneen 800-900 for a bit and then go to 600 and wan to die. pretty much though once it gets into that low idle, it will stay there until cold again OR I unplug the ISCV. the only thing I could think of that could be wrong with the ISCV is that it is out of alignment or something and it closes too much or something.

Who knows at this points.....I am really quite depressed at this point over it...I SO BADLY just want to enjoy this car again.

[jondee86]

The ISCV is a 3-wire rotary solenoid valve. It gets 12V on the center pin
and the ECU pulls one or other of the outer pins to ground. It is a modulating
valve, so the control signals are PWM... more voltage and the valve opens or
closes further. I have tested mine here with straight 12V on the pins...
- 12V to ground on RSO and the valve hits the full open stop.
- 12V to ground on RSC and the valve hits the fully closed stop.
- No voltage applied and the spring returns the valve to the middle position.

Now I guess (and its only a guess) that if the RSO wire wasn't getting the
proper signal, the valve could sit somewhere south of the middle position
and not be able to lift the idle when commanded by the ECU. On my engine
which runs the same ISCV albeit with an aftermarket ECU, if the engine rpm
drops low, I can hear the ISCV open suddenly and suck air to push the idle
back up. It happens plenty quick enough to catch an engine on the verge of
stalling. At other times, it is more just a small change in the sound of air
being drawn in.

For control purposes, when the engine is idling, the ISCV runs in closed loop
with the rpm signal from the distributor. The ECU has a target figure and
will modulate the ISCV as required to keep the engine rpm on target. I would
expect this to hold good even with one dead cylinder, although catching the
engine speed fluctuations might make the valve work a bit harder.

Bring on the test ECU

Cheers... jondee86

[jondee86]

Just while think of it, and we are in clutching at straws mode... if you can
unplug the ISCV and the idle speed jumps up to normal, the ISCV has to be
getting a wrong signal. That is, it is being pushed low.

So is there any chance that the RSC and RSC wires are crossed ?? Maybe even
try changing them over to see what difference it makes ?? Got to be worth a
crack while you are waiting for the ECU

Cheers... jondee86

[bigbacon]

yea I can hear when the ISCV is open because it whistles as it sucks air through the little filter on the end of it. It definitely never opens again when it is idling really low.

[bigbacon]

Ok...

did the O2 sensor tests except for the resistance test on the sensor itself.

Not sure what to make of it.

So I followed the steps, i counted a fluctuation based on when I saw OL on the meter

It was definitely more than 8 times in ten seconds which says normal. Measuing the voltage though on VF1 and E1 was always 2.5v

the BGB testing either says 0V or 5V but it was always 2.5v all the time either at idle or revving to 2500 and holding or even above 2500.

Now the first step on FI-69 says measure voltage while manitaining 2500rpms with the check connrector unplugged. if more than 0V replace it but since it passed the flucuation test I should have never even been at that step which is what is confusing.

I moved on to the other steps just to see what the response was from the meter

If that is normal then the O2 sensor seems to be functioning properly.