Adrian

A couple of points with the ISV.
1/ The ISV fitted to the later model 964s and 993 has the muffler assembly. The one fitted to the 1990 964 does not. Plumbing revisions have to be made and again the there will be be issues with the DME software. The 911 series of DME idle schedule is not as good as the 964 series DME idle schedule.
Add aftermarket unknown chip into the equation and we are in the twilight zone.

2/. The 993 ISV is designed to run with the Bosch 2.10 and 5.2 DMEs. I have heard about the "claims" but I have not yet seen any 964 owner present any credible evidence that they have fitted such a 993 ISV and adjusted it to solve the problem. The 993 has far more advanced software than the 964 and in some areas better sensors installed. Throttle position is much more accurate in the 993 because it uses a potentiometer style sensor rather than throttle microswitches. You can see it clearly onthe 993 wiring diagrams and it even gives you the resistance ranges.

I think Jason you are just going to be running around and around in circles. You will have to bite the bullet.
I would strongly recommend you install the standard chip for the 911 series DME. At least this will give you the correct software for your model and a known starting point.

Nobody can possibly help you with this unknown chip in the DME.
I also warn you that if this chip is what I think it might be it will be causing fault code 1141 to be logged. I am not a betting man but I bet it is a 1141 job (as I call them). Code 1141 means the DME has picked up an internal control unit failure. If this is the case NOTHING with the Bosch hammer will work and this path will also be a huge waste of time and money.

One last thing with these flywheel/clutch kits for general information.
MANY tuners install aftermarket kits but put on the invoice the genuine Porsche part numbers. It is very hard to discover this until you pull the puppy apart again. Believe me I have seen it more times than I wish I knew about.
Sadly they often charge Porsche prices and use the false OEM explanation. What they have done is installed an equivalent but provided the original part numbers on the invoice.
I always ask for the packaging the part was delivered in.
Jason do not be surprised if when you pull this puppy apart that the flywheel etc does not have a Porsche part number anywhere to be seen.

Remember as with many other industries Tuning is a licence to print money. It is so easy nowadays to load a chip up with data and sell it off to eager customers wanting 5000HP out of a 90HP engine for 50 bucks. I have seen downloadable data map files offered over the internet for these chips for up to 2000 bucks.
Ciao,
Adrian.

PS: What are the dates on these invoices?
This story of yours is so so familiar, I wonder if this is the same car and its problems being recycled on this forum with a new owner? The complete lack of personal information about yourself is also disconcerting.

Dunasso

Wow, Christer!!
I'll repeat after you and repeat after me, then we can all jump in and say MOTEC.

jagerocks

I found out today that the flywheel is a single mass 993 RS and the clutch disc is a RS disc, NO TURBO PARTS AS I WAS TOLD AT 1st. Maybe this is good after all. Autothority said they can adjust the ISV and install there chip to fix problem 100% , the cost is $795.usd. maybe this is the way to go.?? What do you think Jason and Arian?

Thanks Jason

jagerocks

They say there is a adjusting screw with epoxy covering it.?? go figure, At Autothority they seem to know what they are talking about.

JasonAndreas

For the $795 they want to do this job you might want to try it yourself first. There are instructions posted in the 993 forum that we might be able to sorta follow, the 993 ISV has 3(?) screws and we only have 1. In the photo below, the red arrow points to the screw. If you dissolve the epoxy I think you'll need a 4mm allen head.



I'll give it a try tonight...

Adrian

A couple of points,
1/. There is no such thing as a 993 Carrera RS LWF. The 993 Carrera RS Clubsport (read track racing car) was fitted with the 964 Carrera RS LWF.
The Basic version of the Carerra RS is fitted with a DMF as is the GT-2.
2/. No further comment.
3/. If you attempt to adjust the ISV what you will do is adjust the mechanical valve stop which will increase the idle rpm thereby not fixing the problem but covering it up with a whopping high idle rpm of around 1000 to 1100 in order to try and catch the drop. Sometimes it will and sometimes it won't and do not try and use the air con.
4/. No further comment.
5/. It is your money.
6/. What a waste of time.
Ciao,
Adrian.

jagerocks

Thanks, I see what you mean, I took the ISV out today and will clean it and go from there.
Jason

Dunasso

Jason keep us up to date, as to your success. I've heard about that method and am interested to see how things turn out.

Duncan

jagerocks

Thanks again for all who helped me out in this prob, Jason,Adrian,Duncan.....

Later Jason

jagerocks

I have cleane dthe ISV and tried to remove the epoxy covering the set screw (which is brass and breaks off) but I don't know if will work yet. Hopefully tomorrow I will get a chance to try it out. I will let all yo know the results.
Jason
1990 C2

AJKOK1

Guys, been away and just picked up on this thread.

I Had my stock 964 fitted last year with a lightweight flywheel and new clutch, the kit was supplied to me by 9m ( ninemeister) in the Uk. I had read a number of previous threads on the potential problem for stalling, but being my usual pig-headed self, still went ahead.

The kit was fitted by another Porsche Independant nearer to where I live, they fitted the kit, and yes the idle was prone to dropping away, they recommended I get all my injectors cleaned as this often exasberated the problem, I agreed and they were all removed and cleaned. Since that time ( and before I had a remap) the problem has been non-existant during normal daily driving.

The only time I experience an idle issue is first thing in the morning if the engine is really cold, the first time i drive away when its cold, and stop at a junction it would stall....my advanced solution, whenever I start her up, i sit for 3 mins to get a bit of temperature in the engine, then off i go and I haven't had it stall for 6 months.

I haven't adjusted my ISV, or pretended I have the A/C on all the time, and my stock idle speed is just under 900 revs.

Could be I am lucky, but my best advice would be to make sure what you have is all ok before you start making more fundamental changes to your setup. For a nominal cost ( or a few hours of your time) get your Injectors cleaned...it made a big difference to me once the LWF was fitted.

Hope this helps

Al.

JasonAndreas

HERE are the instructions for modifying the 993 ISV from Tom Weber & crew on the 993 forum. I'm still waiting for the snow to stop falling before I can start playing around with this in the driveway.

jagerocks

Al,
Thanks for the heads up, I will try that. and clean the injectors.

Jason

Lorenfb

"If you attempt to adjust the ISV what you will do is adjust the mechanical valve stop which will increase the idle rpm thereby not fixing the problem but covering it up with a whopping high idle rpm of around 1000 to 1100 in order to try and catch the drop. Sometimes it will and sometimes it won't and do not try and use the air con." - Adrian -

Adrian is right on!

Obviously, the source of the problem is the deceleration of the RPM, i.e the
rate of change of the RPM which causes an undershoot of the static idle RPM. This
undershoot in many cases causes the engine to stall. Yes, there's a static idle
RPM which will minimize the undershoot, but this will result in an undesireable high
idle, e.g. causing premature clutch wear, in addition to a "super" high A.C. idle.

The DME unit, as with most fuel injection systems, shuts the injectors off when the
RPM is greater than 1200-1500 RPM and the throttle switch is closed, thereby reducing
excess HCs on decel. This feature contributes to the undershoot.

The key to the proper solution is to modify the DME code to "allow" the ISV to open
sooner and gradually bring the idle down to an acceptable value of 900 to 950,
i.e. making a virtual mechanical dashpot as used on older engines. Also, increasing
the injector turn-on RPM to a higher RPM, e.g. 1400 -1600 would help too.

The ISV mod as suggested in some posts would be more problematic on Tiptronic
cars, as it would yield too high of an idle resulting in undesireable "klunks" when placed
in gear. As mentioned, a properly running engine will help minimize the undershoot,
e.g. too lean a mixture (incorrect AFM setting or low fuel pressure). Obviously, the idle
switch must close properly too.

Bottomline: The lighter the flywheel the more difficulty in preventing the undershoot.
I think Andial has been mentioned as having a 964 modified idle chip for a lighter flywheel.
Autothority, I thought, has closed its doors. Is this true? If not, $800 is a lot to "roll the dice".

Cupcar#12

as far as custom Chips go call steve at Rennsportsystems.com - he might be able to come up with a custom chip to help the issue. ( a sponsor of Rennlist)
Also call AASCO performance (they might have made your Flywheel) 714-758-8500 or (714)758-0209
IMHO - 12lbs is ok for a race car - but 19 is the target for a street car.

not associated etc.....