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1990 Porsche C2 - Idle Control Valve

I'm new to this 911 forum, as I just purchased a 1990 Carrera 2 and need advice.

I changed the ICV last night (it was diagnosed as the reason for my high idle rpm) and when I re-started the car I noticed the idle immediately dropped to 650 rpm and notice that it wants to cut out when I come to a stop. I'm guessing I need to "turn the idle" up but my manual does not direct me to this procedure.

Where can I find documentation or assistance to solve this low idle problem I'm now encountering? Any help with diagrams or pictures would be appreciated...
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SAM DACOSTA
1990 Porsche 911 Cabriolet (964)
2000 Porsche Boxster (986)
2002 Porsche 911 C4S (996)
Old 06-29-2009, 03:01 PM
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Have you driven the car very far? I think your DME needs to adapt to the new ISV, mine was the same after cleaning the ISV but was great after a ten mile drive.
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Old 06-30-2009, 01:37 AM
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1990 Porsche C2 - Idle Control Valve

I re-installed the "old" ICV this morning. The low rpm caused many stalls yesterday at traffic lights and stop signs. Very frustrating. With the "old ICV the car idles at 1100 rpm and other than drives well. I'm told it should operate at between 800 - 950 rpm. So until I get further assistance (books, forum, etc.) I'm leaving it alone.

Are there any detailed books or repair manuals that someone can recommend for me to purchase to assist in this and future routine repairs and adjustments on this model Porsche?

"Klr10" thanks for the response to my question. I did drive awhile after changing out the ICV, and I think it would have been enough to allow the DME (?) to adapt to the new ICV. I'm not even aware of the terminology DME? I have allot to learn about this car and it's nuisances....
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SAM DACOSTA
1990 Porsche 911 Cabriolet (964)
2000 Porsche Boxster (986)
2002 Porsche 911 C4S (996)
Old 06-30-2009, 09:46 AM
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Hi, the DME is the brain that controls the engine (injectors, spark plugs, etc,etc). I'm sure everyone on this forum would recommend you grab a copy of Adrian Streather's book all about the 964. That is where many of us gained the bulk of our knowledge. Good luck fixing your car and welcome to the gang!
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Old 06-30-2009, 11:05 AM
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BTW it sounds like your old ICV maybe stuck open, (it's a valve that the DME uses to regulate the engine speed at tickover). It's possible that you have two problems, and that fixing one is causing another to be unmasked. Have you checked that the throttle microswitch is working correctly, it's where the cable attaches to the engine and should be closed when your foot is off the gas.
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Old 06-30-2009, 11:10 AM
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"Klr10" it had occurred to me that something was not right after switching out the ICV. Reason; from my understanding the valve did exactly what it was supposed to do, "reduce the idle speed to around 850 rpm" and it held it there without any surging idle issues. It's during the driving process and coming to a stop (or slowing down) the tachometer falls rapidly below 400 rpm and stalls out. The engine restarts immediately and the idle is stable at 850 rpm but again upon coming to a stop it stalls out.

I realized I needed more information, and knowledge to proceed and decided to put in the old ICV and educate myself and seek guidance before I create more issues that I know not how to fit. LOL

Thanks for the recommendation on Adrian Streather's book on the 964. I will heed your advice and get a copy for myself.

The "Throttle Microswitch" is new terminology to me and therefore I'll get back to you on that after I read about it and see what my expertize can determine. I'll look on previous articles on the forum about this switch and consult the manual and see where I stand. Thanks always for the tips.
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1990 Porsche 911 Cabriolet (964)
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Old 06-30-2009, 11:41 AM
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BTW post some pics of your car or point us at a website. (need to do that too)
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Old 07-01-2009, 09:15 AM
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Oh and checkout www.rennlist.com too... (can I say that?) hope so
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Old 07-01-2009, 09:17 AM
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1990 Porsche C2 - Idle Control Valve

"Klr10" yesterday I purchased a "Haynes Automotive Manual" and got a "Porsche Technical Manual" by Bentley Publishers and ordered the "Adrian Streather, Porsche 964" book. I started reading through a section relating to the "ICV" and now have a better understanding of what it does. The "throttle micro switch" that you mentioned earlier will be addressed this weekend. After some adjustments with the idle speed the "old ICV" now seems to work well, as the car idles between 950 rpm and 1000 rpm. I will continue reading and post results and ask questions as they become apparent.

Thanks again for the tips. Here's a picture of the car in question....




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1990 Porsche 911 Cabriolet (964)
2000 Porsche Boxster (986)
2002 Porsche 911 C4S (996)
Old 07-01-2009, 11:15 AM
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Hi Sam,

Can you describe where the idle speed adjustment screw is on the 964 throttle body? I have seen pics of 3.2 throttle bodies but can't see anything on my cars 3.6 throttle body that looks like an idle adjustment screw.

Thanks,
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Old 07-01-2009, 06:07 PM
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Quote:
Originally Posted by EarlySport View Post
Hi Sam,

Can you describe where the idle speed adjustment screw is on the 964 throttle body? I have seen pics of 3.2 throttle bodies but can't see anything on my cars 3.6 throttle body that looks like an idle adjustment screw.

Thanks,
The "Bentley Publishers, Porsche Carrera 964" book that I purchased showed pictures of the "throttle plate" (which sits atop the "throttle housing") and identified the "air by-pass screw" to adjust the idle speed. The "Haynes Porsche 911 Manual" also identified this as the right screw.

Remember, I'm the newbie here and this is what I'm working with (trial and error). After fiddling with it, the idle speed came down to a desirable level. I was careful to turn in small increments (1/4 turns) so that if it did not work I could at least re-set it back to what it originally was.

Good luck (I guess).
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1990 Porsche 911 Cabriolet (964)
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2002 Porsche 911 C4S (996)
Old 07-01-2009, 06:56 PM
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Quote:
Originally Posted by EarlySport View Post
Hi Sam,

Can you describe where the idle speed adjustment screw is on the 964 throttle body? I have seen pics of 3.2 throttle bodies but can't see anything on my cars 3.6 throttle body that looks like an idle adjustment screw.

Thanks,
Yesterday I received the long awaited "Porsche 911 - Enthusiast's Companion Book, by Adrian Streather and immediately went to the section on "Idle Control Valve (ICV)" and learned they called it "Idle Speed Valve (ISV)" and not ICV. No big issue there but learning proper terminology will assist when discussing repairs and asking questions.

Here's my understanding from this book: "Engine idle speed is set at 880 +- 40 rpm and cannot be adjusted."

When I read that, I immediately wondered what was I was adjusting to change the idle speed earlier. It was called an "air by-pass screw" and mentioned in the Haynes manual and the Bentley publishers, Carrera 964 Book. I then re-set the screw back to the original settings of how I bought the car.

So it seems my original post on setting the idle speed was WRONG and that's what you get for listening to a newbie like me .

I took out the old ISV, cleaned it again per the instructions in the manual, re-installed it and have identified another potential problem (mentioned earlier in this thread by "Klr10"). It seems the reason the car is not idling properly (that is with the new ISV installed) was the "Idle speed micro-switch (closed throttle switch)" could be bad. I say could be because i have not yet tested it per the instructions (just a thought though).

So hopefully this clarifies my mistake and offers some more information relating to the topic.
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Old 07-08-2009, 11:37 AM
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Quote:
Originally Posted by klr10 View Post
Hi, the DME is the brain that controls the engine (injectors, spark plugs, etc,etc). I'm sure everyone on this forum would recommend you grab a copy of Adrian Streather's book all about the 964. That is where many of us gained the bulk of our knowledge. Good luck fixing your car and welcome to the gang!
I'm not aware of what book you're talking about? whats the title?
Old 07-08-2009, 02:38 PM
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Quote:
Originally Posted by geoffjarvie View Post
I'm not aware of what book you're talking about? whats the title?
The book being talked about (or at least the book I purchased from Performance Products) is called; "Porsche 911, Enthusiast's Companion, Carrera 2, Carrera 4 and Turbo 1989-1994" by Adrian Streather.

I just got it yesterday and scanned through it and it had allot of detailed orientated articles specific to the 964. The last comment I made and the information shared about the ISV was referenced from this book.
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Old 07-08-2009, 02:45 PM
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Quote:
Originally Posted by EarlySport View Post
Hi Sam,

Can you describe where the idle speed adjustment screw is on the 964 throttle body? I have seen pics of 3.2 throttle bodies but can't see anything on my cars 3.6 throttle body that looks like an idle adjustment screw.

Thanks,
Idle speed can not be adjusted for a 964. Idle speed is controlled with the ICV and the digital motor electronics. There is no adjustment screw.
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Old 07-08-2009, 04:22 PM
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Quote:
Originally Posted by cjoenck View Post
Idle speed can not be adjusted for a 964. Idle speed is controlled with the ICV and the digital motor electronics. There is no adjustment screw.
Firstly, I'm barely 1 month into ownership of a Porsche 964, so I'm by no means an expert on anything Porsche 911.

I mentioned that in post # 12. When I was asked the question, I answered based on information I read in the Haynes Manual (which mentioned an air screw adjustment). Then yesterday when I received a copy of Adrian Streather's "Porsche 911, Enthusiast's Companion Book" it mentioned 'NO ADJUSTMENT OF IDLE IS POSSIBLE.'

Post #12, was then written to correct the statement. Not trying to be a genius here, just trying to work through issues and ask questions for assistance.
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Old 07-08-2009, 04:38 PM
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[QUOTE=SAM DACOSTA;4752459It's during the driving process and coming to a stop (or slowing down) the tachometer falls rapidly below 400 rpm and stalls out. The engine restarts immediately and the idle is stable at 850 rpm but again upon coming to a stop it stalls out.
[/QUOTE]

Sam

First - I have a TIP, so this is not from first-hand experience:

Many posts have discussed the problem of low idle and stalling. The concensus is the replacement of the clutch/flywheel ass'y to a "lightweight" one. The new one doesn't have the rotational mass to keep the engine running when going from high revs to idle.

There are aftermarket chips that address this issue. Search here and on RL and you should find good reading on this subject.
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Old 07-09-2009, 03:54 AM
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Quote:
Originally Posted by LouZ View Post
Sam

First - I have a TIP, so this is not from first-hand experience:

Many posts have discussed the problem of low idle and stalling. The concensus is the replacement of the clutch/flywheel ass'y to a "lightweight" one. The new one doesn't have the rotational mass to keep the engine running when going from high revs to idle.

There are aftermarket chips that address this issue. Search here and on RL and you should find good reading on this subject.
As always, I appreciate any tips, or any assistance I can get.

I have an RS Clutch and assembly installed, so that might not apply to this particular scenario. However, I'll be searching "RL" and this "Pelican Forum" for any discussions on the topic. I have an aftermarket Chip but have decided to wait to install it, as I want to understand the car and it's nuisances before I encounter upgrade issues (or potential issues.)

Just an update. After the cleaning of the ISV (2 days ago) and now driving the car today (40 miles) the car now idles closer to what's tolerable (950 rpm). I will continue to pursue this topic (even just for further knowledge on the 964).

Thanks.
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Old 07-09-2009, 07:22 AM
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A chip with suitable code will definetely help.

The other item of importance is the operating point of the ICV and the idle mixture.

You may have noticed the throttle body has an adjustment for the lower stop of the throttle plate. Depending on its adjustment the ICV will do whatever is required to keep the RPM around the 840 value. If the lower throttle stop is missadjusted then the ICV is not in its sweet spot and might not have enough "leverage" to catch falling RPM's fast enough. The results are stalls.

Then there is the idle mixture adjustment screw in the AFM body. The AFM will give different reading depending on how much air this screw lets bypass the barn door.

You need a hammer (Bosch 9288) or PST-2 tester to be able to read the ICV duty cycle at idle and adjust things properly.

Ingo
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How about a NoBadDays DualChip for 964 or '95 993
Old 07-09-2009, 08:20 PM
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Quote:
Originally Posted by ischmitz View Post
A chip with suitable code will definetely help.

The other item of importance is the operating point of the ICV and the idle mixture.

You may have noticed the throttle body has an adjustment for the lower stop of the throttle plate. Depending on its adjustment the ICV will do whatever is required to keep the RPM around the 840 value. If the lower throttle stop is missadjusted then the ICV is not in its sweet spot and might not have enough "leverage" to catch falling RPM's fast enough. The results are stalls.

Then there is the idle mixture adjustment screw in the AFM body. The AFM will give different reading depending on how much air this screw lets bypass the barn door.

You need a hammer (Bosch 9288) or PST-2 tester to be able to read the ICV duty cycle at idle and adjust things properly.

Ingo
This is good information and I thank you for sharing your knowledge. I'm looking at the idle issue again this weekend and will take into account what you have mentioned in your post.

Questions though; regarding the parts listed, where are they purchased and cost if you know? I'll be checking with Pelican Parts catalog later to see if they sell it but if you knew off hand you could just share it...
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Old 07-10-2009, 10:02 AM
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