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86 synchro high idle.
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BRUNKBOX
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PostPosted: Tue Apr 24, 2007 6:17 pm    Post subject: 86 synchro high idle. Reply with quote

I've just got this van running (did not run when i bought it. Engine was replaced by previous owner and never completly connected). The idle bypass valve gets a constant signal from the ecu (DIGIFANT - YIPPIE) , so the idle is really high and I can not adj the distributor. If I unplug it I can start to play with the distributor. What inputs does the ECU need for it to operate the idle stabilizer valve? Little help please I don't want to go CARB but I will if it means a running van.
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Captain Pike
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PostPosted: Tue Apr 24, 2007 6:30 pm    Post subject: Reply with quote

The "brain" for the stab unit is in the pass wheel well. OHM it for faults, they do fry......
Did you hunt for vacc leaks first??
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Dogpilot
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PostPosted: Tue Apr 24, 2007 6:35 pm    Post subject: Reply with quote

Your first step is to ensure that the Throttle switch is doing its job and you have NO vacuum leaks. If it works correctly and you don't have any leaks, then you do the timing-idle-jumble. The timing has to be in the proper range to set the idle speed, mechanically. one somewhat affects the other, so a bit of back and forth is required. Once that is done, then you can do the electronic settings.

You can set the mechanical idle by unplugging the signal to the idle computer. THere is a black connector on the fwd firewall, it resembles the connector for the O2 sensor. You unplug it, and now you can set the idle speed mechanically. the speed is adjusted by the big slot screw on the throttle body. reference where you start, so you can go back. Once you hae it running at around 850, you can follow the proceedures for setting the idle computer's speed.

Read these, they are in the stickies in the manuals online, digifant section:
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08 Range Rover SC
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BRUNKBOX
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PostPosted: Tue Apr 24, 2007 6:50 pm    Post subject: Reply with quote

Thank you for your responses , I will check all this soon and get back with you all. Working for a living gets in the way of so many things you know. Thanks.
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Yellow Rabbit
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PostPosted: Wed Apr 25, 2007 10:40 am    Post subject: Reply with quote

You have to be sure that the connector for the idle control valve and the throttle switch are not reversed. I have heard of people plugging one ito the other and frying the throttle switch. It seems that if you have a constant signal to the idle valve, this could be your problem.
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tencentlife
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PostPosted: Wed Apr 25, 2007 11:46 am    Post subject: Reply with quote

On a Digifant, those two connectors are not interchangeable. The TBS connector is 2-pin, and the ISCV is 3-pin. Swapping them would surely cause damage if it were possible; the two signal circuits are at widely different voltages.

The TBS does switch on the ISCU, so it must be closing at idle to have it work. That is a 5V signal supplied by the FI ECU (so don't try jumping 12V to it).

Other inputs the ISCU shares with the FI ECU are system voltage (which is power supply), starter trigger 50, rpm, and coolant temp. It also receives 12V triggers directly from the AC clutch and PS pressure switch.

You can disable the ISC system a number of ways, it doesn't matter which, so you can set up your timing and base idle speed and CO. The book recommends unplugging the single rpm signal wire at the forward bulkhead. You can also unplug the 3-pin from the valve, or remove the controller from its holder plug (it is behind the plastic wall at the base of the right D-pillar duct, forward of the right taillight). I find it easiest to unplug the valve connector.

If with the ISC disabled, you still can't get the idle down to 900, you could have vacuum leaks, too much fuel pressure at idle (check regulator), excessive resistance in the coolant temp sensor circuit, or an overly worn throttle body. The first three are self-explanatory and easy to check and remedy. Good luck with the worn TB, though, decent replacements are harder and harder to find. There some remedies in the stickies.

Just because the ISCV is humming does not mean that the system is functioning correctly. The best test is the results test: idle the car, note that the rpm should be about 900, put it in gear, and slowly ease out the clutch until it drags. The idle speed should not drop.

The technical test is to measure the milliamp signal at the valve connector. This is a pain to set up for most people, and doesn't tell you much more than the function test will. If your geekiness is in ascendance, then by all means, be my guest....

Oh, and you can't set the ISCU's speed. It regulates the opening frequency of the ISCV (the humming) to maintain a preprogrammed speed. Once it is getting all its various inputs, it either works, or it doesn't.

The ECU itself has a basic program that can maintain a good steady idle when warm if basic tuning is set right. The ISC system merely modifies the volume of idle air, acting as a dynamic throttle bypass. If it doesn't function, you can run without it. You just won't have idle boost on warmup, and when the AC clutch is cycling or the steering is at full lock.
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BRUNKBOX
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PostPosted: Wed Apr 25, 2007 6:43 pm    Post subject: Reply with quote

Man you guys are great, this will be a weekend of testing. Just so you know I replaced the throttle switch (it was all corroded inside ) and checked the throttle assembly (shaft seems tight no lateral play). No vacuum leaks found or heard. The engine runs about 3000 rpms at idle (close as I can get to setting timing) but like I said soon as I unplug the ISV It comes down to something reasonable. I pulled apart the ISV control unit and found no obvious damage.
Is there information on doing pin (ohm, pwr, grnd) tests at the ISV control unit? I will also check the fuel pressure because with ISV unplugged and engine running It will just stop running after a few minutes. It will only restart if I disable the fuel pump (like mabe it was running to rich) and soon as it tries to start I engage fuel pump again and engine runs. I ran a toggle switch to the fuel pump relay ground wire and a jumper wire to the starter for testing purposes while I'm in the engine compartment (this is helpful). Any ways thanks again and I will keep you updated.
** P.S. if any of you all own a new generation MINI COOPER (R50, R52, R53 & R56) and have any questions please hit me with them. This is what I work on. **
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Dogpilot
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PostPosted: Wed Apr 25, 2007 8:03 pm    Post subject: Reply with quote

You should get the entire protraining manual and work thorugh the systems one at a time to see what works right and narrow it down. If you want to get a pdf version, look on my download page for a copy of what you can read online:
http://homepage.mac.com/WebObjects/FileSharing.woa...mp;lang=en
You want Vanagon Protraing Digifant and Vanagon Protraining Fuel Systems They are not that long to print out for a hard copy.

Your regulator may be going bad, try this test as well:
Image may have been reduced in size. Click image to view fullscreen.

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86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G
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tencentlife
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PostPosted: Wed Apr 25, 2007 8:08 pm    Post subject: Reply with quote

Hmmm, sounds like you may have the same problem as this fellow:

http://www.thesamba.com/vw/forum/viewtopic.php?t=227105

There are also some threads in the stickies about testing the fuel pressure and replacing the fuel lines.

High fuel pressure will contribute to a high idle. I think from what you're describing that your pressure regulator is sticking closed or there is blockage in the fuel return line.

If all that were OK (it sounds like it's not) , a 3000rpm idle with the ISC system connected pretty much says that the ISCU is bad. The main ECU rarely goes bad, but the ISCU makes up for that by failing religiously. My local VW wrecker says he can't keep them around; they go out the door as soon as he gets one because so many folks have to replace theirs. I got a used one from him recently, but it was bad, too. Raised the idle right to 2000rpm.

The pin connections are on Bentley p.97.107 for a 1987. All the Digifants are the same.

The pin tests (based on the tiny embossed numbers on the face of the ISCU connector base) are:

#2: test for continuity to single connector branching off from the AC clutch connector, red/blue connecting to a white/green wire. Check for continuity with the white/green. Or check that pin 2 goes hot when AC clutch engages.

#4 and #11: these should have continuity to one each of the pins at the ISCV connector (only two pins in a 3-pin connector). There is no polarity.

#5: ground.

#6: #50 starter trigger signal. Goes hot when starter is cranking. Also common to ECU pin 1.

#8: 5V present when TB switch closed with engine running. This is the signal to turn on the ISCU. Common to red/yellow wire at TB switch. Also common to ECU pin 11.

#13: coolant temp signal. Continuity to the white wire at the Temp2 sender plug, and to ECU pin 10.

#14: battery voltage when ignition switched on. Should also be common to one of the two wires at the PS pressure switch, and to ECU pin 14.

#15: Continuity to the other PS switch wire.

#17: continuity to the green wire at the diz connector for the Hall generator. I think it's the center wire there. Also to ECU pin 18.

I think that's all of them. As you can see, several of the signals are shared with the ECU.

But run your fuel pressure tests first.
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