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The ISV modification for LWF

 
Old 06-12-2004, 05:41 PM
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Jonster
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Default The ISV modification for LWF

Looking through the archives, I found several references to a method to modify the ISV (Idle stabilisation valve) so it could be used to modify the idle speed on the 993 for use to lessen the problems associated with using a LWF (light weight flywheel) I also wanted to do it to increase the idle speed so that the alternator would charge properly, as my engine is running the 993RS/Patrick motorsport pulleys, which run the alternator slower.... seeing as the 993RS idles at 950 RPM for this fact, I thought I would try to get my idle speed also up the 950 (at which speed my alternator starts to behave just as it should do) rather than the current idle speed which is about 820 rpm/

After a lot of tralling, and searching, I managed to find some details for this... but find that on my 993 setup, as soon as I adjust the ISV by so much as a degree, the engine instantly gasps and cuts out.

Does this indicate that I have a fault somewhere (as I suspect) or, have other members found that on some 993 setups the alteration of the ISV causes the car to cut out as soon as the unit is adjusted away from the stock adjustment?

It seems almost as if the adjustment of my ISV is increasing the air available to the engine side of the throttle body, which should increase the idle speed, but for some reason the ecu is not providing additional fuel to allow the engine to run with any additional air until the throttle moves... or, that at idle, the engine is running so lean, that any additional air causes it to immediately cut out.

Any thoughts?

Jon
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Old 06-12-2004, 08:16 PM
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jon - couple thoughts.

1. have you cleaned out your isv valve? on mine there was a lot of carbon build up and cleaning it out is an absolute must. I spent a good 1/2 hr with carb. cleaner and a 1/2 roll of paper towels.

2. you want to make sure you are adjusting it about 5-6 degrees counter clockwise. also make sure that the you have at least one of the screws in (not tight) as you rotate the white ****.

3. on mine if rotated it too far the idle would wander way up and way down. but it didn't die.

hope that helps - let us know...

as a sidenote, i also have the patrick motorsport RS pulley setup and mine is a '95.

Cheers,
Boris
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Old 06-12-2004, 09:32 PM
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John D.
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Hmmm - I just did this.. Today....

First - Boris is exactly right - mak certain your ISV is absolutely CLEAN before doing any adjustments......

Second - if Tom is reading this - my thanks....

Third - ready? Do this:

Remove the ISV and scribe the metal and the grey plastic so you can get back to the original setting...

Next - take a sharp SMALL jewelers screwdriver, and remove the epoxy from the 3 holes you'll see. Under the epoxy are 3 allen screw heads. Clean enough epoxy so you can get to the screws.

Next - loosen the screws a bit, and turn the plastic part (the electrical connector) about 3 degrees COUNTER CLOCKWISE.

Next - tighten one screw head so nothing moves.

Next - reinstall the ISV and start the car.

Next - if the idle isn't right (mine is set at 890) - loosen that one screw head, and turn the base (the grey part that the electrical connector is molded into) about 1 degree. Let the engine settle.

Next - repeat the previous step as needed. If you go too far - turn it back, and start over - the ISVs are VERY sensitive as is the idle as you adjust it...

Next - when you are set - tighten all three heads.

That's it.

JOhn
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Old 06-12-2004, 10:00 PM
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Jonster
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Hi Boris,

The ISV is super clean, I spent ages cleaning it, filling it with carb cleaner, shaking it, pouring it out, cleaning some more...

With your Patrick motorsport pulley, did you find the stock idle was a little too low to maintain a good idle charge rate from the alternator? My one is idling at about 820RPM and it just does not seem to be enough to get a charge from the alternator, but when I bring it up to 900 RPM or more, it goes up to 13.8 volts.

Hi John

Thats exactly what I am doing... at my scribed stock setting I get about 820 RPM, if I turn it about 2 degrees counter clockwise, you can hear it sucking more air, and the idle does increase by about 20 to 30 rpm, but it runs really rough... take it any further than that and you hear a big gasp from the air filter and the engine dies. I have also tried moving it by a degree at a time.

Can you think of anything that may be wrong with my engine, engine management or sensors which would make this happen?

Did either of you guys remove your battery and get the engine to re-learn its new idle? or would that make it over ride the increased idle?

Jon
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Old 06-12-2004, 11:23 PM
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Hi Jon:

I am the guy who originally posted the ISV adjustment.
I couldn't find my original post in the archives.
I've received many private emails reflecting
positive results from this adjustment.

It is important that the ISV is completely cleaned and
that your internal aperture door is moving free.
If you shake the ISV, the internal aperture will bounce
magnetically until it stabilizes to a small pre-set opening.
You should not feel any grinding or hear any sounds
as this would indicate worn or sticking ISV bearings.
Turning the mechanism counter-clockwise should do the trick. You can observe the aperture
opening and closing after you loosen the three 2.5MM bolts.
Turning counter-clockwise will open the aperture, thus allowing
more bypass airflow, and turning clockwise will close
it, causing an engine stall.
Over-adjusting will cause the idle to loop wildly and
uncontrolled, as the computer will attempt to get it
down to a specific value. Make sure you make a
scribe mark on the plastic connector to the
ISV housing before you start the adjustment.

I also extended control of the ISV by adding an electronic
circuit that raises the idle about 100 RPM while driving in
reverse and when stopped on an upward hill.



All the best,
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Old 06-13-2004, 12:09 AM
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david,

can you describe the electronic circuit
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Old 06-13-2004, 12:11 AM
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jon -

my patrick motorsport pulley setup doesn't seem to hurt the charging. but i also have an optima battery. no issue at all....

Cheers,
Boris
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Old 06-13-2004, 03:10 AM
  #8  
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Boris:

Attached is the schematic and description. I posted this
back in February. So far, the circuit continues to work
as intended.







A couple years ago, I posted a DIY on how to adjust
the Idle Stabilizer Valve. Many Rennlisters followed
the instructions and had positive results as it solved
their stalling issues.


Recently, I expanded on controlling the ISV.
I incorporated a circuit that increases the idle speed
about +100 RPM when stopped on a steep upward hill
or when the reverse gear is engaged. I installed this
circuit in my '97 C4S and it has worked well.

However, it may respond differently in other vehicles
due to ISV conditions and production parameter
variance. It also requires proper and safe construction
and installation. Given these conditions, I cannot
guarantee it will work to complete satisfaction.
I must also stress if constructed, that it is used in a
responsible manner. Also, some modifications can
be construed as a disclaimer for existing warranties,
or automatically fail an emission inspection, or even
cited as a safety violation in the event of a disputed
accident -even if the modification is not relevant.

I invite those who wish to comment or expand on this
idle speed control concept.

Driving conditions for circuit operation:

1. Car is facing an upward hill greater than four
degrees while the foot brake is engaged.

2. Car is operated in reverse.

1. We all have experienced the embarrassing and
potentially hazardous situation where our engine stalled
at a stop light on a steep hill. It's often difficult to
determine how much clutch control and pre-revving is
needed to properly engage without burning the clutch or
stalling the engine. As a result, we all choose to burn
our clutch a little in order to avoid a stall.

2. It's also difficult driving in reverse as we have limited
vision making us too pre-occupied with safe driving and
not enough concentration with pre-revving and clutch
control. The reverse gear ratio is 2.86:1 while first gear
is at 3.82:1 respectively. By comparison, reverse gear
is almost the same ratio as second gear.


The method of detecting driving conditions:

For detecting steep hills, a mercury contact switch is
utilized and positioned to turn on if the car is stopped on
an upward hill greater than four degrees. The mercury
switch will only increase the idle speed if the foot brake
is applied and the steep angle is detected.

The method for detecting reverse gear is a connection
to the reverse back-up light.


Modification circuit description:

The modification circuit utilizes a power MOSFET and
current limiting resistor that act like a soft "on-off" switch.
When the FET is turned on, the current limiting resistor
provides a small biasing current on the aperture opening
side of the ISV, thus causing a small increase on the
opening of the aperture resulting in an increase of about
+100 RPM in idle speed. The "on" signal coming from
the reverse light, brake light, and mercury switch are
connected to a series resistance and isolation diodes
that are connected to a capacitor that charges up in
about 0.5 seconds. This slow charge turns on the FET
enabling the increase idle through the ISV. If reverse
gear is dis-engaged, or when the car approaches level
ground, or the foot brake pedal is released,
the activation voltage to the capacitor is disconnected.
The stored charge on the capacitor is discharged
through a slow discharge resistor. The resultant slow
discharge of the capacitor allows the FET to maintain
higher idle for about 5 seconds, before the circuit
disconnects. This provides plenty of time for needed
increased idle while letting in the clutch. The slow
response times of the modification circuit also allows
the DME (Digital Management Electronics) to maintain
proper ISV control, without disrupting the DME feedback
control loop.

Values of most components expressed are not critical
as changes to the values will only vary response times.
It is not recommended to decrease the value of the
50 Ohm 5 watt resistor* as this will result in disruption
of the idle control causing uncontrolled oscillations and
looping of the idle speed, as well as possibly logging a
fault code error with the DME idle positioner control.
*( 47 Ohm 5W is O.K)

The preferred design would be a linear progressive
idle control with varying angle positions and controlling
the idle at the master clock inside the DME.
Eventually, I plan to design such a circuit to further refine
this idle control. But for the time being, this simple
circuit is performing the job.
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Old 06-13-2004, 04:10 AM
  #9  
Tom W
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David,

I'm one of many who used your original post to get my ISV adjusted for my LWF. I have a copy of it if you'd like it. I edited your information and a couple extra bits from tom_993 into a document I send to folk who ask for it (John D was the latest).
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Old 01-22-2006, 12:20 PM
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THIS PLACE ROCKS.........

I've been fighting this prob for months...took me less than an hour to complete this job and Ruby humms.....

Bumped for those in need.......
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Old 01-22-2006, 01:00 PM
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mpgandco
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I have been trying to adjust mine and have probably tried at least 20 times.If I move it even just a tick counter clockwise it bumps idle a little,but it hangs up at about 1200 rpm for a few seconds and then drops to about 850.If I turn it back to thr original setting it doesn't hang up anymore but the idle is not increased.I have also noticed that if I turn it at all the car will surge while trying to drive at about 3000 rpm.Any ideas,is my isv worn out?I have stated I have moved it back and forth and always the same result,the idle hangs up for about 10 seconds and then settles down.Any ideas
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Old 01-22-2006, 01:55 PM
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One thought ... I sounds like you guys are doing this with the ISV connected and the car running. I did my adjustments with the car off - adjust, start car and see how it goes, turn off and readjust, repeat. You might see if that make a difference.
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Old 01-22-2006, 01:58 PM
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Tom you have PM
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Old 01-22-2006, 01:59 PM
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I have done all my adjustments with the ISV removed
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Old 01-22-2006, 02:32 PM
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David,

Thanks so much for sharing this. Could you maybe post this post into the DIY section that we now have on Rennlist? I may need it in the future! ;-)

Cheers,

David
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