-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, 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
Last edited by davidgracevan; 12-07-2011 at 06:20 AM.
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
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.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 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
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
1985 5-speed window cargo van set up for llama haulin'; 345K ("Trustyvan")
1989 4WD 5-speed DLX; 410K and an odd sense of humor ("Skylervan")
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.
Sounds like the aux air valve is working properly then; I would leave it alone. Unless of course you're willing to risk another problem (the one I referred to, and it's a pain) ...
Gwen
1985 5-speed window cargo van set up for llama haulin'; 345K ("Trustyvan")
1989 4WD 5-speed DLX; 410K and an odd sense of humor ("Skylervan")
Reviving an old thread here -- the quote above are the symptoms my van is experiencing right upon startup, so I was curious if someone could expand on what causes this as it seems to have been brushed over in this thread.
For more info: on cold starts, the van typically starts fine (sometimes with a sporadic RPM, but nothing major and no odd noises/feelings from under the hood), but once the engine is warm it will stutter with large RPM drops acting like it's going to stall out, though usually doesn't, and/or it will stutter and stumble to it's start. It also tends to idle low when warm. Once driving I have no issues. I read through this thread and this one and this one, but am feeling a bit overwhelmed with all of the different valves and valve names and technicalities. I saw this thread which seems to be my same problem, but it had no information on it besides a possible FPR fix. Google tells me these symptoms are common to a faulty IACV (hence why I'm posting in this thread), but the info here seems to counteract that (also I'm not sure which one of the valves on our vans is the IACV).
Curious if anyone has had this same issue and successfully solved it? And/or could share some thoughts on what might be causing this? I recently cleaned my throttle body (which was very gunked up) as a first thought, yet the issue persists. It definitely seems to be an air-related issue to me, but I'm a newbie and could definitely be wrong.
Hello, and thank you van gurus for this incredibly helpful thread. I’ve had ongoing cold start issues since I resurrected by 85 Van last year. I’ve narrowed it down to everything but this air valve. Cold start time switch is good (was replaced along with the Bosch connector), cold start injector passed ohm test and is confirmed to be working, I cleaned my throttle body when I did the TPS, I replaced all vacuum lines and verified there are no leaks, I even tried a spare ECU since I had one from the junkyard.
And still, when cold starting I got to put my foot on the throttle a little to get it to start. Otherwise, it’s exactly like Gwen describes here, I’ll hear it fire up but promptly die. I followed the on-vehicle check outlined on page FI-57 (that was quite a stretch with the longest pair of pliers I had) and it failed. No change in RPM.
So last night I pulled my intake and got the air valve out, and unfortunately it looks good, as illustrated in the repair manual??? Looks just like my other one, open just slightly at room temperature. Ohms are the same on both too, at 44.
I’m wondering if anyone knows a little more specifics about how these work. Like what’s the 7mm adjustment screw do? Does the heat coil change with coolant temp and then move the gate valve accordingly? If so then what is the actual electrical connector for? Or does it run off the ecu temp switch (which I have also replaced)? Lastly has anyone experimented with rebuilding these using parts from other Toyota air valves? I looked around online and it seems like other models had air valves just with different shapes.
I’m taking my fuel injectors to be cleaned and tested and I’m waiting on an intake gasket from rockauto, so I have a little while to figure out what I’m going to do. I would hate to put my new/old air valve in and have the same problem. Any input would be greatly appreciated, this forum has been a lifesaver.
So I'm having this issue when I start my 1991 Previa. It would die if I didn't give it gas when cold until I set the idle up higher to prevent that. It can go up or down a bit (±200rpm) as I'm driving if I'm in neutral at a stoplight after it's warmed up but it works fine for now.
I took off the throttle body and cleaned it up as it was pretty dirty (cat safe cleaner), as well as removed & cleaned the ISC (I tested it with 12v and it seemed to open/close fine) & put on new gaskets for both. The problem is still there. I have replaced the fuel filter in the past when I had the issue before but I believe it was only an issue at stop signs since it's a manual and not idling low on startup like it is now. That was only a few years ago and it's a messy affair so I'm hoping to avoid that. I'm going to do a cap/rotor/wires/plugs tune up soon to rule that out since it's been 60k miles. (I'm at 407k miles!)
On a side note, I did pull a bonehead maneuver (I know really stupid) and pulled out the MAF sensor (or VAF sensor) which yanked on the "serviceable" soldering connections about 2 months ago. It wouldn't start at all and found this video showing me to pull off the jumper wires and just solder the pins straight to the board and it worked! I'm assuming that it has nothing to do with this issue as it ran fine for at least a month and a half before this issue popped up. This guy saved me a long drive to the junk yard. https://www.youtube.com/watch?v=CXCpYj-r_lI&t=714s
Not 100% sure this is related to the thermostat, but my 87 4x4 5sp has been idling really high once warmed up (after 5 minutes or so). It hasn't been overheating, and other than the constant sound of a revving engine when in neutral or the clutch is engaged, it's driving normally. A friend mentioned it could be a thermostat issue. Has anyone had this issue before?
If the van warms-up and the heater blows hot air, then it's not related to the thermostat. It could be a failed air valve (between the intake manifold halves). When the coolant is cold, the air valve allows air flow (increases idle speed). When the coolant is hot, the air valve closes and prevents air flow (slower speed). To test, warm the van, then pinch an air tube going to or from the air valve. If the idle speed goes down, then you have a failed air valve. Tim
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