993,951,944

I wanted to let everyone know that the 993 idle stabilizer valve is adjustable. When properly adjusted, the results are more bottom end torque and a more stable idle. I only recommend this if your engine is functioning correctly, but the idle is still too low and unstable. I can provide some details if anyone's interested.

All the best,

David

mags993tt-home

That sounds interesting. My idle is stable but I feel it is on the low side. Is there an 'official' fully warmed up idle speed for the 993 + tt (if different) that I can check against?
M

kevin993c4

David,

My idle is definitely a little low. Please advise.

993,951,944

O.K here's the Idle Stabilizer adjustment:
Remove the idle stabilizer valve.
( Clean it as well )
Remove the epoxy covering the three Allen head screws on the plastic electronic connector side.
Make a scribe marking on the aluminum stablilzer
body to the plastic connector side to mark the
original factory position. Loosen, but do not remove, the three Allen screws. Grip the aluminum body and grab the plastic electrical connector and turn the internal mechanism 2-4 degrees counter-clockwise. ( a little less than the distance of one minute on a clocks hand.)Yes, this
adjustment is very sensitive! If you can't turn the mechanism, you can use a wrench to increase the grip but be very careful not to damage the connector plastic. Note that by rotating the valve you can see the internal door increase and decrease aperture. Re-install the valve with the three Allen screws slightly loose.
Start engine and note the idle speed. If it's too
high, turn the valve back by turning the electrical connector side (With electrical connector attached) to the factory position, using the scribe marks, and let the engine warm up to normal temperature.
Once the temperature is at normal, slowly turn the valve counter-clockwise until you hear the idle increase slightly. The computer will automatically compensate for the valve position but will allow for some adjustment.
Do not over-adjust as this would result in dangerously high idle and "looping" from computer
compensation as well as out of spec emissions. Once the optimum valve position is determined, tighted the three Allen screws to hold
the valve in the new position. Take a test drive and determine if the idle is normal under all conditions. Repeat adjustment if needed.
Use the scribe mark to return the valve to the
factory position if the results are not helpful.
Otherwise, reward yourself with a warm beverage for a job well done !

Good luck !

David

smithk993

Without a doubt, I would love to adjust my ISV. After putting in a lightweight flywheel and chip I still have problem with stalling. I would like to increase the idle speed by 100-150 rpm and see if this helps.

Thanks for the info. Please email to this post if you would prefer.

Keith

smithk993

What did you use to remove the epoxy covering the screws?

993,951,944

Hi Keith:

To answer your question, I used a sharp very small
screw driver to chip away the hard epoxy. Yes, there is an Allen screw (three total) under all that epoxy. You'll need to leave the screws inside as they keep the plastic outer piece in alignment with the inner mechanism. You'll see the results on how the aperature opens and closes as you rotate the mechanism. Work into the adjustment slowly as I hear replacement
ISV's run $100-$200. So be careful !

Good luck Keith,

David

KASH '95 993

Keith, keep us posted on your stalling issue if you make the adjustment. Thinking about installing the light weight flywheel myself; however, just don't think I can put up with the stalling issues associated with the MY95 993's. Thanks,

Pete Lech

David, thanks for the tip. I have cleaned my ISV, btu I still get a little bobble at idle, which goes away when I turn the AC on. I tried different gasoline brands to no avail, so this will be next.

tom_993

If you have stalling problems with a LWF, read this post:

David,
Thanks very much for sharing this knowledge. I experimented with it over the weekend and got good results. I had thought that my mechanic made this adjustment when I had my flywheel installed, but when I looked at the ISV, there was the (factory appearing) epoxy covering the screws. While I don’t have stalling issues due to having a mid-weight flywheel (Andial’s version), pushing the clutch in would cause my rev’s would drop like a rock to about 600, then blip up to 900 or so, then finally settle down to about 700 (all rev numbers are from the dash tach, which isn’t necessarily the most accurate). After making this adjustment, the revs drop to 900 or so, then slowly drift down to the original 700. If anybody has stalling problems with their LWF, I highly recommend that you do this procedure.

Another very beneficial side effect to me is that this appears to lessen the surging that I (and others) have reported previously. I’m talking about the lurching you get when you go on and off throttle at parking lot speeds. Part of this is caused by compression braking when you come off throttle and the computer cuts fuel. I think by making this adjustment, the compression braking isn’t as strong, as the engine slows down slower. This did not make the problem go away, but it does appear to make a significant improvement. Of course, I’ve only driven the car once since I made the adjustment, so time may prove me wrong. It could also be my imagination.

A couple of comments on the procedure. It went almost exactly as David states. I tried a screwdriver to get the epoxy out, but quickly found that unproductive. I have a tiny little dentist drill sized grinder attachment for my Dremel tool. This took the epoxy down to the top level of the allen screws in a matter of seconds. The trick is to get the epoxy out of the head of the screw without rounding it out. Since the epoxy is much softer than the steel of the screws, a very gentle touch with the Dremel takes the epoxy away without grinding the screw. You’ll need a 2.5mm Allen wrench for the screws. Once I loosened the screws, the mechanism was stuck. I used a large crescent wrench to loosen it. The size and shape spread the force over a large area, and it doesn’t have teeth to mar the plastic. With the wrench, it came loose easily. I made the 2-4 degree adjustment and put it back in the car. I’d say skip this step, as you’ll need to do the adjustment with the car warm and running. With the car running, as you move the connector, the idle will go up and down. I got it as high as 1000 RPM, but finally tightened the screws when I had it set a bit higher than 800. I think the computer does make an adjustment. It seems that turning the car off then back on will cause the computer to re-compute the idle and set the ISV accordingly, as my idle always returned to about 700. Perhaps I’ll experiment further by setting the idle at 900 or so and see what happens when I turn the car off then back on.

Thanks again,
Tom

E. J. - 993 Alumni

Great report guys. I appreciate it as I have the true LWF sitting in my garage waiting for the clutch to go away. Maybe I can fix it at Mid Ohio next week?

E. J.

993,951,944

[quote]Originally posted by tom_993:
<strong>If you have stalling problems with a LWF, read this post:

David,
Thanks very much for sharing this knowledge. I experimented with it over the weekend and got good results. I had thought that my mechanic made this adjustment when I had my flywheel installed, but when I looked at the ISV, there was the (factory appearing) epoxy covering the screws. While I don’t have stalling issues due to having a mid-weight flywheel (Andial’s version), pushing the clutch in would cause my rev’s would drop like a rock to about 600, then blip up to 900 or so, then finally settle down to about 700 (all rev numbers are from the dash tack, which isn’t necessarily the most accurate). After making this adjustment, the revs drop to 900 or so, then slowly drift down to the original 700. If anybody has stalling problems with their LWF, I highly recommend that you do this procedure.

Another very beneficial side effect to me is that this appears to lessen the surging that I (and others) have reported previously. I’m talking about the lurching you get when you go on and off throttle at parking lot speeds. Part of this is caused by compression braking when you come off throttle and the computer cuts fuel. I think by making this adjustment, the compression braking isn’t as strong, as the engine slows down slower. This did not make the problem go away, but it does appear to make a significant improvement. Of course, I’ve only driven the car once since I made the adjustment, so time may prove me wrong. It could also be my imagination.

A couple of comments on the procedure. It went almost exactly as David states. I tried a screwdriver to get the epoxy out, but quickly found that unproductive. I have a tiny little dentist drill sized grinder attachment for my Dremel tool. This took the epoxy down to the top level of the allen screws in a matter of seconds. The trick is to get the epoxy out of the head of the screw without rounding it out. Since the epoxy is much softer than the steel of the screws, a very gentle touch with the Dremel takes the epoxy away without grinding the screw. You’ll need a 2.5mm Allen wrench for the screws. Once I loosened the screws, the mechanism was stuck. I used a large crescent wrench to loosen it. The size and shape spread the force over a large area, and it doesn’t have teeth to mar the plastic. With the wrench, it came loose easily. I made the 2-4 degree adjustment and put it back in the car. I’d say skip this step, as you’ll need to do the adjustment with the car warm and running. With the car running, as you move the connector, the idle will go up and down. I got it as high as 1000 RPM, but finally tightened the screws when I had it set a bit higher than 800. I think the computer does make an adjustment. It seems that turning the car off then back on will cause the computer to re-compute the idle and set the ISV accordingly, as my idle always returned to about 700. Perhaps I’ll experiment further by setting the idle at 900 or so and see what happens when I turn the car off then back on.

Thanks again,
Tom</strong><hr></blockquote>


Hi Tom:

It sure made my day that you received good results from the ISV adjustment. Don't forget
the final and critical step of rewarding yourself with a warm beverage.


All the best,

David

tom_993

Update: I guess I was too conservative with my original settings. By moving the internal mechanism a little more, I was able to get a consistently higher idle. I was able to get it to stay at 1,000 RPM’s, which was too high, but it was a useful experiment. After further tweaking I’ve been able to get my idle to stay at 850 or so consistently. The car is even better now. I still get a little “leveling out” of the idle when I push the clutch in, but it’s a blip of 50 to 100 RPM, not 300 to 400. The lurching is still there (I would pay big money to get rid of this), but it’s less.

And David, remember this is Southern California! It’s warm here, so we celebrate with cold beverages! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> Thanks again for sharing this knowledge.

Tom
'95 993

993,951,944

[quote]Originally posted by tom_993:
<strong>Update: I guess I was too conservative with my original settings. By moving the internal mechanism a little more, I was able to get a consistently higher idle. I was able to get it to stay at 1,000 RPM’s, which was too high, but it was a useful experiment. After further tweaking I’ve been able to get my idle to stay at 850 or so consistently. The car is even better now. I still get a little “leveling out” of the idle when I push the clutch in, but it’s a blip of 50 to 100 RPM, not 300 to 400. The lurching is still there (I would pay big money to get rid of this), but it’s less.

And David, remember this is Southern California! It’s warm here, so we celebrate with cold beverages! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> Thanks again for sharing this knowledge.

Tom
'95 993</strong><hr></blockquote>


It sounds good Tom. Here in Western Washington,
we drive in cold rain and rush-hour traffic.
However, at least we can find some comfort in knowing how to drink our coffee...

Keep monitoring your ISV adjustment, you may need to back off the RPM's if you ever experience cold weather in California.

All the best,

David

CosmosMoon

Ok, so yes, this is a 22yo thread that I’m reviving! I just wanted to say - thanks for posting this - it works! I have a midweight flywheel, and had an ECU tune to take care of the idle but I had to revert my ECU to stock and was looking for ways to fix the idle and came across these instructions.

good thing about the car being 25+ years old now is that the epoxy is very brittle, and I was able to pick it out with a dental pick pretty easily. I turned the electronic part about 2 - 3 degrees enough to up the idle from about 750 to 850 and I have no more stalling when moving around parking lots or the driveway - sweet! This is so easy and so easily reversed provided you mark the top before turning it. I also found it very easy to turn once the screws were loose.