-our van's engine has an ISC valve, when does this operate or turn on?
-our van's engine has an ISC valve, when does this operate or turn on?
There is an ISC VSV (Idle Speed Control Vacuum Switching Valve) that's controlled by the ECU. It's a solenoid operated air valve that when activated allows a small amount of air to bypass the closed throttle body valve. The result is an increase in idle speed of about 100 RPM. The ECU is programmed to complete the circuit (provide ground) to the ISC VSV when certain conditions are met. 12V positive is supplied to the ISC VSV from the AM2 ignition circuit when the EFI main relay is active.
-thanks sir Tim, my ISCV was already missing, i want to restore it back, when do the ECU turns this ISC valve on?, in what situations do this ISC turn on?
That's a secret :LOL2:, well, it sort of is. Toyota never bothered to talk much about this in the service manual so I'm not sure what these predetermined conditions are. They talk about the ISC VSV in the very end of the FI section, but there's only a simple schematic and a brief description on how to test it. I wish the manual would elaborate on this more, but it doesn't. Tim
:LOL2: well i found this in the internet... http://www.autoshop101.com/forms/h26.pdf . based from what i read there, what i like to know is that do our ECU turns this ISC on when we shift the transmissin to Drive? coz mine RPM drops to 500-600 when shifting to drive or reverse... does it also turn on when for example theres a heavy electrical load?... what do you think sir Tim?
As far as ECUs go, ours are some of the earliest (and most primitive) ones out there. When it comes to control systems it's all about input vs output. I don't think ours are sophisticated enough to detect electrical loads (but I could be wrong). I'm not sure what year range that article is referring too, but some of the standard functions in today's ECUs weren't even thought of back when ours were built. Tim
-ok sir Tim thanks for your thoughts. You have an A/T van right?, do yours drops rpm when the gear selector is shifted to drive or reverse?
FWIW, my rpms drop, somewhere close to the amount you mentioned, when I put my van in gear.
Couldn't tell you how it was originally. Only had mine for just under two years now.
-is it originally like that sir? RPM drops when shifting gear?
-does the ISCV compensates the RPM lose when shifting the van in gear?... guys can i hear your experiences about this ISCV?... thank you :)
-can anyone help me out here?.... thanks
wow, tim doesnt even know what it does?!?!?!
LOL :dizzy:. I only know what I read in the manual (posted above). Whatever the manual doesn't cover becomes speculation. As far as I know the kind of "van specific" information requested isn't covered in any publications I know of. If anybody else has more information please post it here. Frankly, I don't think such information is necessary to correctly troubleshoot and repair the van, but it would be helpful for the troubleshooter/mechanic to fully understand the system. For me it's much easier to understand and troubleshoot problems when such information is available. I wish there was a van specific book that explained what was going on in the engineer's heads when they designed the system. I can get into that kind of reading :drool: (not sure what's wrong with me) :dizzy:. TimQuote:
Originally Posted by gushaman
-i'm just wondering sir Tim, does your van with A/T lose rpm when shifted into gear?
Yeah, it's normal for the engine to slow down a bit when it has a load placed on it. I never really paid much attention to it so I couldn't tell you how much.......say 100-200 rpm??? The van I drive every day does not have a tachometer. Tim
-ok sir Tim, it loses 200 rpm, if following the service manual, we should set it the idle at 750, right... shifting the gear, rpm goes down to 600-500 which i observed stresses the alternator because it is not turning at optimum speed especially during night time when it is really loaded, i just thought that it supposed to be the job of the ISCV but it turns out to be not. Some of our guys here suggested that idle should be set at 1000 so that when gear is shifted, it will at 750. i tried to set my idle at 1000, it makes the shiftshock a bit harsh... what do you think sir Tim?
Set it at 750 while in neutral and forget about it. It's normal for our alternators to not charge while at idle. As long as it's not sitting at idle for extended lengths of time (with everything turned on) you will be fine. The system is designed to share the load with the battery. When it's at an idle the battery will help out with loads. When you are driving the alternator takes over and replaces energy that was taken from the battery......it's a give & take set-up. Of course this requires your battery to be in decent condition. If your battery is questionable then you may have problems. If the van needs to sit at idle for extended periods, then turn off the unnecessary loads. Tim
-thanks sir Tim for that urgent reply. you hit it sir, during heavy traffics here, definitely i'll be sitting long at idle, another scene is the very slow moving traffic where you would just crawling and your foot stays at the brake pedal. my battery is new, checked every electrical concerns (keeping voltage drops in line acceptable) but i observed that when shifted to gear, you will notice a slight dimming of the lights, a/c blower somehow drops speed. what i do is to brake with left foot sometimes then put my right foot on the accelerator to raise the rpm back to 750 where everything is working very well. In newer vehicles with A/T, when shifted to gear, the ECU compensates the transmission load and raises the engine rpm back to the predetermined rpm, in our van that does not happen, like what you have said our ECUs a bit of a first age. i believe that the alternator still charges at idle considering before i change battery before, my old battery drops it voltage at 10 volts in the morning after parking at night, starting my engine helps it to bring back to 12 volts, but the rpm should be 750... what do you think again sir Tim?
(P.S. i'm really gald sir Tim that we were able to share our thoughts here :))
Does the battery get too low to restart the van? Unless your battery is going dead it's nothing to worry about.
-no it does not. i think i just worry too much sometimes. keep thingking of effeciency, i was planning to make something that will compensate for the rpm drop when in gear, somekind of added vsv in the engine which activates when gear is not in nuetral or park. oh well, thank you very much sir Tim.
Keep in mind that higher RPM with vehicle stopped (and in drive) equates to additional energy loss due to drag and more heat/wear to the transmission due to increased slippage. Of course we're talking small amounts, but I think this would be more than enough to offset whatever benefit you may get from "electrical system efficiency". Bottom line is "if it ain't broke, don't fix it". Tim
- thank you sir Tim for a reminder. i'm just trying to imitate the newer A/T s of toyota, studying how the toyota's ECT works, it could be applied to the van. innovating and trying to improve van's capabilities. i really love it so much. thanks again sir. i'll be posting if the plan was a success. :)
i dont suppose there is an option for an under/overdrive pulley for our alts? i know some performance folks use larger or smaller pulleys to make things spin faster/slower. I do know the van alt has a small pulley
I suppose if you were using the van for a purpose other than what it was designed for AND problems arose, then perhaps there would be merit for making changes. In my life there are enough problems to deal with that are urgent. Unless I ended up walking home I wouldn't consider this one of them.
Yes, you could possibly speed up the alternator. Then you have to wonder how fast is too fast? What if by messing around with it you traded a non-problem for a real one??? :doh: Just saying :lol:
-thanks guys for the infos and reminders. i'm not just looking at the alternator's effeciency, i'm also looking at the engine's effeciency. studying our van's engine, it runs effeciently at 700-750 rpm, lower than that we can notice that it idles a bit rough, a noticable vibration will be felt, thats why i'm aiming to imitate the Electronic Controlled Transmission of Toyota in the newer vehicles to help the engine run at optimum, and also will help the alternator run at its optimum... theres no bad trade to see... as you have said sir Tim, our van's engine management is a bit primitive, thats why i'm trying to improve it by adding components that you can see at the newer age vehicles... :)
This was an interesting thread to read. Although I must say if you are looking to mimic what is going on in todays cars, it might be a better Idea then trying to make old work like new, just find a local junk yard (not u pull it or pick a part). They usually get autos that have been in wrecks and such, find one that hasn't been sitting long and is Newer model and do a swap i mean as long as you get the PCM and TCM you could just have a shop make motor mount adapters and voila you got a sweet modern engine.
Now that I've installed a new TPS and adjusted the idle speed to 750 rpm when warm, my van runs and idles great except for one thing: when I first start it cold, it'll die if I don't hold the throttle open a bit for a minute or so. After that, all is well. Does this sound like a cold start injector problem? Or maybe a timer controlling the cold start injector? Advise on this would be much appreciated.
Could be this, could also be a faulty air valve. In the FI section of the factory service manual there are tests for both of these. The cold start injector time switch is tested using an ohm meter. The air valve is tested by removing the hose (when cold) and trying to blow through it. It should allow flow when cold but prevent it when engine comes up to temp. Tim
Thanks very much. I'll have a go at testing both of them. I'll let you know what happens .
Linn
Linn, did you get 'round to testing those components? I'm curious to know if you identified the problem.Quote:
Originally Posted by linnharding
Thanks for following up. I'm embarrassed to say I haven't dealt with the problem. Throughout the summer, I only had to hold the throttle down for 10 seconds or so and that was just too easy. My trusty van isn't seeing much action these days since I got a 2000 Honda Insight. It needed a $25 dollar transmission input shaft bearing and I got the car for $1000 so this has become my main ride these days. 65 mpg is average, 75 if I work at it. I'll get back to my van soon and when it's fixed, I'll post it.
Thanks again for following up.
Linn
I have the same problem. its hard to start when cold. i have to step on the gas for about five seconds. Tim dose that sound like a cold start valve? i tested the ohms and it was 5.6. the books says between 2-4 ohms. could that throw it off by being 1.5 ohms over? i have not tested the timing switch for the cold start vavle yet. what do you think Tim?
I see in your signature you only have a Previa listed........so I gotta ask are we talking a Previa or a van? If Previa, please post your question in the Previa Tech section. If you are asking about a van, then we're good. You should read through the FI section of the manual as it gives detailed answers to your questions. I'm a little confused with your terminology. When you say "cold start valve" are you talking about the CSI (Cold Start Injector) or the Air Valve? The CSI should have a resistance of 3-5 ohms. If I saw a reading of 5.6 I would say it's probably okay (Electrically anyhow........that doesn't mean it's not clogged or leaking).
Another component that affects cold idle speed is the Air Valve. The air valve is sandwiched between the two halves of the intake manifold. It should be partially open when the van is cold. You won't be able to visually see this when it's installed, but you can find out by pinching one of the tubes that goes to it. When the engine is cold, start it up and pinch a tube (best one attaches to the bottom side of the throttle body intake tube............it's the bigger one that goes towards the rear of the engine). Use a pair of long nose vice grips or something similar to pinch it off. When cold you should see RPM's drop with the hose pinched. If the RPM's are already low it may stall (this is an indication the air valve is good). If RPM's do not change then the valve is bad. After it warms up, pinch it again. This time it shouldn't drop but up to 50 RPM's is allowed. If RPM's drop more than 50, then the valve is bad. The electrical connector for the air valve is accessible from the front of the intake area below the cold start injector. When warm (about 180 deg) the resistance on it's terminals should be 40 - 60 ohms.
The Cold Start Injector Time Switch is mounted on the driver's side of the coolant filler neck. Here's a copy/paste from the manual to show how it's tested. Tim
http://i8.photobucket.com/albums/a23...ps75556a30.jpg
Sorry about that Tim. I own only a Previa. It was however for my friends mom. She has an 88 le van with only 65k on it. I didn't think it was any thing major. It was just a clogged fuel filter. I guess it has never been changed all these yeas.lol anyways yeah one of the guys here at my job called the cold start injector a cold start valve. After looking online its an injector, so ill smack my friend at work for calling it a valve and making me look like a fool.lol
My van idles pretty rough in the cold when I start it up. Does any one have the part number of the idle air control valve? Im thinking about buying a new one from toyota and seeing if it makes the van run smoother.
These are expensive and hard to replace so I would test and verify it's bad before replacing. It's Toyota part #22230-73011. MSRP is $281.17 or it can be purchased via a discount internet Toyota parts site for ~$200. www.rockautoparts.com used to have aftermarket ones until recently (probably sold out), but you can still get on eBay: http://www.ebay.com/itm/New-Kyosan-A...a59fd1&vxp=mtr. It's mounted to the underside of the top intake manifold & requires the upper manifold to be removed in order to replace. Tim
I don't believe my air valve is working. the van idles the same cold and hot. The 2 pins ohm out as good.
How much does the air valve raise idle when the van is cold, if its
Attachment 4623
I want to eliminate it while my intake is off if its not working or not getting signal.
Anything to reduce the complicated plumbing and eliminate vacuum lines.
Thanks!
When you start the van, does it run rough and want to die (or actually die if not given gas)?
Gwen
No but I have to floor it to make it start in less than 30 sec of cranking.
(probably a separate issue, Fuel safety switch or 5th injector.) happens regardless of summer or winter.
I need someone to squeeze their hose while the van is cold and see how much RPMs drop.
Part of this is evaluating if the air valve is worth having. (faster warmup is all its providing.)
I could rewire the AC idle up switch for a selectable high idle.