Idling at 1K

toml

toml

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Jul 24, 2005
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Been following this thread and learing quite a lot, so firstly: thanks to everyone posting here.

Now, my understanding is that the ISC valve is the only passage of air into the intake manifold when the TB is closed. So, blocking the ISC Valve's air pipe (from the accordian pipe) should cause the engine to die because it no longer has any air.

So what should happen if you unhook that pipe between the ISC valve and the accordian pipe? You're leaving the ISC valve open, so there's still air getting into the manifold, but the air it is getting is not metered by the AFM so I'm assuming there's something bad going to happen there.

My first thought was that the engine was still getting air, so it'll keep running... but I'm not sure any more.

Thanks. :)


ps. I have the same outcome as jonathan1 when I turn my wheels at idle, the RPM drops from 650 to about 550. Is this normal or is my P/S idle-up valve not working correctly?
 
johnathan1

johnathan1

Supra =
Aug 19, 2005
5,056
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Downey, California, United States
when I unhooked the ISCV pipe, the idle got a little choppy, but it was still okay...when I plugged it, it didn't really make any difference, just kept idling like normal...

This is really enfuriating me... I have checked pretty much everything, and the idle is still weird, and i have no codes... I also replaced that P/S idle-up hose, and it didn't make any noticeable difference... I just about every hose in the vacuum system...with the ISCV blocked off, and the idle didn't change!

*sigh* I think I'll just go sit in the corner and babble incoherently, whilst drooling and contorting uncontrollably...
 
3p141592654

3p141592654

90T
Oct 11, 2005
3,816
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Thousand Oaks, CA
As covered above, the ISC is not the only air source that bypasses the TB. There is also the PVC (which has a fixed orifice), the PS idle-up, and all the vac accessories (brake booster, heater control valve, cruise control, EGR control, turbo pressure sensor and so on). A leak in any of those will impact the idle speed although the ECU will compensate as much as it can by closing down the ISC.

It is normal for the PS to drop the idle a little as you note. The idle up only cuts in at full lock to stop the engine from stalling when the pressure goes sky high.
 
bigaaron

bigaaron

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Apr 12, 2005
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toml said:
Been following this thread and learing quite a lot, so firstly: thanks to everyone posting here.

Now, my understanding is that the ISC valve is the only passage of air into the intake manifold when the TB is closed. So, blocking the ISC Valve's air pipe (from the accordian pipe) should cause the engine to die because it no longer has any air.

So what should happen if you unhook that pipe between the ISC valve and the accordian pipe? You're leaving the ISC valve open, so there's still air getting into the manifold, but the air it is getting is not metered by the AFM so I'm assuming there's something bad going to happen there.

My first thought was that the engine was still getting air, so it'll keep running... but I'm not sure any more.

Thanks. :)


ps. I have the same outcome as jonathan1 when I turn my wheels at idle, the RPM drops from 650 to about 550. Is this normal or is my P/S idle-up valve not working correctly?
Click to expand...


The ISC is not always open. The isc is only used to adjust the idle rpm when it is too low. The ISC is the only way the ecu can adjust the idle rpm. The engine would not always just die if you blocked the ISC input off. The rpm might just decrease.
 
bigaaron

bigaaron

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toml said:
Oh I see... well I pulled off the ISC pipe and the engine immediately died. Is that normal? :)
Click to expand...

That is probably because you created a big vacuum leak after the afm, not because you closed off the ISC. YOu would need to unplug the isc hose and then plug both ends.
 
bigaaron

bigaaron

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I have a breather filter on my isc because it's running map now. You can really hear what the isc is doing. When the engine is cold the ecu opens the isc for fast idle, but after that there is almost no air going through the isc. All this is not all that helpfull anyways because if you were going to bypass your isc you need to open the throttle plate a little bit to make the idle permantly higher so it will not die when its cold.

See in this pic there is a huge vacuum leak created when the bov was disconnected. You would need to block off the fitting on the accordian hose to troubleshoot the bov. A bad bov might be a boost leak but would not cause a fast idle because it is just bypassing the turbo, not taking in unmetered air.
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johnathan1

johnathan1

Supra =
Aug 19, 2005
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Downey, California, United States
well, here's what I just did, I blocked off the ISCV on the accordian and hose... Removed the BPV, blocked the small vacuum line, and the port on the accordian hose, and sprayed a little bit of carb cleaner into the BPV orifice on the 3000 pipe, it made the idle increase everytime I sprayed...that would mean that my throttle plate isn't sealing wouldn't it??
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
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Redacted per Title 18 USC Section 798
Huh? No can read? Stop messing with the CBV (what you're calling the BPV). Just block the ISCV and the PCV port. Does the engine die?

The idle is going to increase anytime you shoot carb cleaner into the manifold because it's a hydrocarbon. You're enriching the mixture.
 
johnathan1

johnathan1

Supra =
Aug 19, 2005
5,056
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Downey, California, United States
But, if the throttle plate were sealing correctly, it wouldn't allow the Carb cleaner to pass through and increase the idle, right? Or am I missing something?

I also tryed what you said...I capped off the ISCV, and the PCV at the TB, and the idle didn't really change that much, went down to like 900...I started pinching every hose I could get my pliers around, and the idle didn't change at all... the idle speed screw is located on the TB, right?
 
bigaaron

bigaaron

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jetjock said:
Huh? No can read? Stop messing with the CBV (what you're calling the BPV). Just block the ISCV and the PCV port. Does the engine die?

The idle is going to increase anytime you shoot carb cleaner into the manifold because it's a hydrocarbon. You're enriching the mixture.
Click to expand...

I think he is thinking that the tb is not totally sealed but I still don't think it matters. It's so easy to tell if the throttle body is not closing all the way. If the linkage is not taught with the pedal not depressed then you can eliminate that as an issue right away. Turn it by hand, you can easily feel if there is anything wrong with the tb.

I have worked on lots of 7m's and in every case the idle was off because of a vacuum leak, timing is off, or tps problem or mis adjustment.
A tps problem will cause the timing to be off at idle. To check for a vacuum leak you can spray the carb cleaner around possible leak locations and if the idle goes up then you found the leak source. You do that with everything connected like normal.
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
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Lol, no argument here. I would've had it fixed by now too. Just trying to help the kid out but a lot of them can't seem to follow directions. As far as old school techniques go this isn't a carbed 65 Impala you know. These things take finess if you don't want to fumble around ;)
 
bigaaron

bigaaron

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Apr 12, 2005
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jetjock said:
Lol, no argument here. I would've had it fixed by now too. Just trying to help the kid out but a lot of them can't seem to follow directions. As far as old school techniques go this isn't a carbed 65 Impala you know. These things take finess if you don't want to fumble around ;)
Click to expand...

I've worked on his car several times trying to help him get various bugs ironed out. He has never changed the tps and I vaguely remember telling him it was sticking but I can't remember. I have seen so many bad tps sensors. Probably 20 in the last year. They get sticky and cause intermittent idle issues. Issues exactly like the ones he is having.
The wiring harness is also about ready to fall off the engine, literally.
 
johnathan1

johnathan1

Supra =
Aug 19, 2005
5,056
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36
Downey, California, United States
Yes, I know this is taking a long time, I've been devoting most of my attention to graduating high school, so the Supra is kinda on the back-burner at this moment, not completely, But I just haven't been devoting my complete attention to it... I will take off the 3000 pipe tomorrow to inspect throttle plate and end the guessing...

JJ: Yea, thanks for the help...I definitely need it ;). As for the carb cleaner, I have used it before to detect vacuum leaks, and it seems to work well...and just seems to be pretty easy/inexpensive...I will agree that it isn't the best way though...

Aaron: Yes, you have been an ENOURMOUS help to me! (Especially when I was fixing my hg ;)) I don't really recall you ever testing my TPS, but of course I could be wrong, and if it is old (like everything on the car), then it is more than likely shot...I will see about testing that tomorrow. As for the wiring harness...yea...it's pretty bad, but what can I say...I can't afford a new one, and this one is still working for me, so...yea.

Big huge applause to JJ and Aaron!!! WOOT!
 
johnathan1

johnathan1

Supra =
Aug 19, 2005
5,056
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36
Downey, California, United States
Okay, I think I may have found the problem...This has to be the part that was making the hissing noise...

I was driving today, and I boosted slightly, let off the throttle, and POW! I heard something pop...here's what it was...
 
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