Idle Stabilzation Valve
04-26-2018, 07:31 AM
#1
Rennlist Member
Thread Starter
Idle Stabilzation Valve
This 993 thread https://rennlist.com/forums/993-foru...valve-isv.html is one of the most technical I’ve read and I’m keen to see what advanced tests can be done on the 964 ISV to improve erratic idle operation diagnosis. Mine is currently fine, which is a great time to get base line data. The only problem so far is that the 964 ISV has 2 pins compared to the 993s 3 pins. Has anyone cut open a 964 ISV?
04-26-2018, 08:27 AM
#2
Burning Brakes
04-26-2018, 05:16 PM
#4
Rennlist Member
Thread Starter
What I'm interested in is the control mechanism. The 993 ISV has a power supply and two control lines, one to extend and one to retract the valve whereas the 964 only has two wires, so logically only one control line. I'd like to understand how the valve position is controlled with one control line.
When I know that I can understand the pulse output of the DME to complete a systems analysis. Too often I see hunting issues that aren't satisfactorily fixed by ISV replacement. I'd like to describe the system so that diagnosis is easier.
When I know that I can understand the pulse output of the DME to complete a systems analysis. Too often I see hunting issues that aren't satisfactorily fixed by ISV replacement. I'd like to describe the system so that diagnosis is easier.
Last edited by John McM; 04-26-2018 at 05:53 PM.
04-26-2018, 06:32 PM
#5
Rennlist Member
What I'm interested in is the control mechanism. The 993 ISV has a power supply and two control lines, one to extend and one to retract the valve whereas the 964 only has two wires, so logically only one control line. I'd like to understand how the valve position is controlled with one control line.
When I know that I can understand the pulse output of the DME to complete a systems analysis. Too often I see hunting issues that aren't satisfactorily fixed by ISV replacement. I'd like to describe the system so that diagnosis is easier.
When I know that I can understand the pulse output of the DME to complete a systems analysis. Too often I see hunting issues that aren't satisfactorily fixed by ISV replacement. I'd like to describe the system so that diagnosis is easier.
04-26-2018, 07:57 PM
#6
Rennlist Member
Thread Starter
Hunting could be due to an ISV not responding correctly to the inputs from the DME or it could be due to incorrect inputs to the DME, or even a bit of both. At its heart it's a simple feedback loop system, with the ISV as the only output, influencing the amount of air entering the engine at idle.
I'm also interested in getting a range of scantool outputs e.g. at idle the Scantool tells me that my ignition is advanced 6.5 degrees at cold start, quickly moving to 5.6 degrees when warming up (my after market ECU used advance as one way of 'catching' a falling idle.
BTW: My adapted IAC trim is 128 (80h), whatever that means.
If I understand how the ISV works and tap into the DME signals on a working idle, then there is a base line to diagnose when it goes wrong with a hunting idle.
Last edited by John McM; 04-26-2018 at 08:20 PM.
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04-27-2018, 07:20 AM
#8
Rennlist Member
Thread Starter
Thanks for that info Rob. By maintaining a constant voltage and varying the pulse width the system is varying the power to the solenoid and therefore its position.
What confuses me is that the 993 uses two solenoids to control the valve. One to open and one to close. I gather the 964 is a single solenoid. Is it spring loaded? I’m guessing that adaptation fine tunes the base solenoid position, like a neutral position which is why the engine must be at operating temperature and all loads off when an adaptation is carried out, as that is the logical point where the least amount of air bypass is required.
What confuses me is that the 993 uses two solenoids to control the valve. One to open and one to close. I gather the 964 is a single solenoid. Is it spring loaded? I’m guessing that adaptation fine tunes the base solenoid position, like a neutral position which is why the engine must be at operating temperature and all loads off when an adaptation is carried out, as that is the logical point where the least amount of air bypass is required.
04-27-2018, 04:09 PM
#9
Drifting
i have removed mine, shot carb cleaner into it and applied 9VDC from a little battery to get the carb cleaner to swish around. (tea came out) It is spring loaded... With it moving back to rest position with voltage removed.
04-27-2018, 05:50 PM
#11
Rennlist Member
Thread Starter
Originally Posted by Laker
i have removed mine, shot carb cleaner into it and applied 9VDC from a little battery to get the carb cleaner to swish around. (tea came out) It is spring loaded... With it moving back to rest position with voltage removed.
04-28-2018, 05:28 AM
#12
Rennlist Member
Thread Starter
To measure the pulse width I need to buy Bosch test kit 1684463093 or VAG1315A/1. Easier said than done and not cheap.
Am I correct in guessing that the ISV plug is a Bosch EV1 fuel injector plug and therefore I can make my own tester with male and female EV1 plugs?
04-30-2018, 02:25 PM
#13
Technical Guru
Rennlist Member
Rennlist Member
And there are six compensation maps for adjusting that (base) amount of bypass, separate to the algorithm/function for trying to get it to match the idle RPM setpoint. And then all the fuel and timing maps to support that. Although those are pretty constant once the CHT reaches its peak value. When we were trying to come up with a solution for the LWF, we noticed that battery voltage and electrical load plays a BIG part when it came time to try and catch a falling RPM when completely off-throttle.
04-30-2018, 04:07 PM
#14
Drifting
With 9VDC applied the valve moves. When the voltage is removed, it flips back to the 'rest' position. Wether is open or closed I don't know.
Shooting carb cleaner into it fixed the issue I had. Starting on a warm engine sometimes stalled and I had to start again.
04-30-2018, 05:44 PM
#15
Rennlist Member
Thread Starter
And there are six compensation maps for adjusting that (base) amount of bypass, separate to the algorithm/function for trying to get it to match the idle RPM setpoint. And then all the fuel and timing maps to support that. Although those are pretty constant once the CHT reaches its peak value. When we were trying to come up with a solution for the LWF, we noticed that battery voltage and electrical load plays a BIG part when it came time to try and catch a falling RPM when completely off-throttle.
I have ordered plugs to make a test lead (actually I had fun finding the male EV1 plug at a reasonable price and ended up with 20!), have a possibly faulty ISV coming to test and am all ears for any more info. It’s really a fact finding mission for me as eventually my idle will hunt and when it does I’d like to have a logic based approach to solving it. I’d also like to write a definitive post as some of the information is spread about e.g. your recommendations on ISV cleaning fluids.
