[Cloud9...68]

Over the past year or so, my 968 has developed a crazy irregular idle.  I promise, I wasn't touching the gas pedal as I was filming this video:

 

(132) Irregular idle - YouTube

 

Other than the goofy idle, the engine runs great - very smooth, and it pulls strongly (well, for a 968, anyway).  I've checked the hoses for leaks, and I actually found a couple with small cracks, but replacing them surprisingly made no difference.  I've tested the idle stabilization valve, and it snaps smartly when I apply 9V across its terminals.  The irregular idle seems to be temperature dependent;  it seems to be worse in hot weather. I have an RS Barn teflon intake manifold gasket, and it's it good condition, and I've confirmed the tightness of all of its bolts.

 

I wish I could do a blink test, but my blink test mysteriously stopped working several years ago.  So before I take it to someone (hopefully with a Durametric), any ideas on what else I should check?  Thanks.

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[unknown4u]

Youtube needs a permit from you for others to see this video....

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[Cloud9...68]

Sorry about that - it's fixed.

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[tejon007]

So, have you checked that there is voltage to the valve? Here's some more suggestions I found (do you have a spare DME to try?):



The idle valve controls the amount of air that bypasses the throttle valve and is variable to allow precise adjustments. The valve consists of a double solenoid; one for opening and one for closing the valve. A power supply is connected to both solenoids and the ground side of each solenoid is connected to the DME. When the DME needs to change the position of the valve, it activates the solenoid by switching the solenoid to ground with a duty cycle signal, which creates a magnetic field that pulls the valve to the new position. The duty cycle value affects the position of the valve and therefore the amount of the air bypassing the throttle valve.



The idle control valve is expensive so before replacing it make sure you perform all neglected maintenance and check things like your O-2 sensors, injectors, MAF sensor and give the throttle body a good cleaning. Some of the problems like stalling on deceleration and stall stops can be caused by a dirty throttle body. The idle stabilization valve is also sensitive to ground faults so make sure to check and clean your grounds especially at the battery and under the driver's seat.



While lots of people will tell you that you can simply clean the heck out of the valve with carb clean and reinstall it; this is not a good long term solution. If you clean the valve and it helps fix the problem then you know that the valve is at fault and it should be replaced. Putting a valve that has been soaked in cleaner back into the vehicle may save you a few dollars upfront but the cleaner will eventually eat through to the coil wraps in the valve and lead to failure, and can on occasion lead to an electrical spike getting back to the DME. If cleaning the valve solves the problem that is a good diagnosis that it needs to be replaced.

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[Cloud9...68]

Thanks - I did a basic check to confirm that the ISV was opening and closing when applying a voltage across its leads, but I didn't do anything beyond that.  I sure wish my blink test were working, because that would help narrow down which sensor or module to look into.  It would probably be cheaper for me to take it to someone with the right diagnostic tool than for me to start randomly replacing parts.  I don't have a spare DME relay, but I'll test my current one, although the symptoms aren't really the ones normally associated with a bad DME relay (hard starting).  The way the idle is jumping up and down looks like a vacuum leak, but I haven't found a smoking gun there yet, either.

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[unknown4u]

Mount an 1.2 watt bulb in the 19 pins connector from Pin.15 to ground, that is the way to have an extern Check Engine Control light.



If you than run the onboard diagnose, you can read the codes if the light on the dash is not working or not installed.
This is for you the cheapest en quickest way for your blinktest.

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[Cloud9...68]

Mount an 1.2 watt bulb in the 19 pins connector from Pin.15 to ground, that is the way to have an extern Check Engine Control light.



If you than run the onboard diagnose, you can read the codes if the light on the dash is not working or not installed.

This is for you the cheapest en quickest way for your blinktest.

Thanks;  But the issue with my blink test isn't that the check engine light isn't coming on, it's that it doesn't blink.  When I move the key to the accessories position, the check engine light illuminates, but when I hold the throttle at the floor for 5 (or 10, 20, etc.) seconds, it never starts blinking.  I've experimented with leaving the throttle depressed for different lengths of time, and nothing makes any difference. It used to work fine, then one day decided to stop working.  I guess these are the types of gremlins you'd expect in a 30-year-old car.

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[unknown4u]

Check if the cable will give you a full throttle. If it only can depressed for 98% the blink-test will not start

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[Cloud9...68]

Interesting;  I wasn't aware of that.  It seems pretty tight, but I'll confirm when I get home tonight.

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[Waylander]

the body of the IVC has an O ring under the metal top cover, mine was in a pile of bits with a massive air leak, a full clean of the ICV take it to bits replace the O ring and has now been fine for 7 years,

the ICV is the same as a Hyundai Lantra 2.0 and is considerable less money, worth a $40 experiment,

 

especially as the correct ICV is now NLA 944.606.161.01, Part dropped from Porsche stock on the 1st of May 2021, and before it was dropped it cost $400

 

for the blink test you need the ignition in the II position so the ignition circuit is powered up, and if its not detecting the WOT position of the TPS then it could also be a faulty TPS

 

and the TPS (Throttle Position Sensor) is a small fortune, if you buy Porsche, but its a Bosch part used on many cars, so have a good look around

 

Porsche Part 944 606 116 00 $429.00, If you search Ebay.com for the Porsche part number any one of the Volvo listings will work correctly, its a Bosch Part $10

 

 

we are going to have to get creative with spare parts as porsche are dropping more and more parts that are unique to the 968, with a run of 12,000 and low perceived values, its just not worth the trouble for them

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[Cloud9...68]

Thanks, Waylander - that's great information.  I will definitely look at the o-ring you're describing.  The fact that the engine runs so well once off idle does point to the ICV valve as a likely culprit.  I removed the AC (it stopped working several years ago, and I didn't feel like spending the money on it when the car is primarily a track car) several years ago, and relocated the alternator to the compressor's position, so my access to the ISV is very good.  Is the o-ring you're describing available as a Porsche part, or did you just locate one whose dimensions match the one in the ISV?

 

I think my TPS is OK, because I tapped into it to monitor throttle position in my Aim data acquisition system (it's primarily a track car), and I checked the voltage put out by the TPS before doing this, and it was behaving normally.  It is very strange how my blink test suddenly stopped working, though.  I appreciate how you guys have given me some things to troubleshoot;  I really want to avoid taking it to a shop.

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[Waylander]

Thanks, Waylander - that's great information.  I will definitely look at the o-ring you're describing.  The fact that the engine runs so well once off idle does point to the ICV valve as a likely culprit.  I removed the AC (it stopped working several years ago, and I didn't feel like spending the money on it when the car is primarily a track car) several years ago, and relocated the alternator to the compressor's position, so my access to the ISV is very good.  Is the o-ring you're describing available as a Porsche part, or did you just locate one whose dimensions match the one in the ISV?

 

I think my TPS is OK, because I tapped into it to monitor throttle position in my Aim data acquisition system (it's primarily a track car), and I checked the voltage put out by the TPS before doing this, and it was behaving normally.  It is very strange how my blink test suddenly stopped working, though.  I appreciate how you guys have given me some things to troubleshoot;  I really want to avoid taking it to a shop.

I just took it to bits, I have a big box of O rings of all sorts of Diameters and cross sections and just found one that fitted, Its not a part designed to be dismantled, of the two hoses to the ICV one is now NLA the other L shaped one is $40

 

the blink test should work as long as you still have the standard Motronic Computer

 

for parts try this

 

http://www.pdlibrary.co.uk/Files/Other/9...erence.htm

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[Cloud9...68]

That's an incredible list of alternative parts.  Did you assemble it yourself?  To state the obvious, it will definitely be a challenge to keep these cars running as more and more parts become NLA - I'm kind of surprised Porsche has kept supplying parts for this supremely obscure model as long as they have.  Even among car enthusiasts, I'd say less than 10% I've talked to about my car have ever heard of it.

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[unknown4u]

For the hydraulic lifters you can use Audi 200. A fifth of the price of the original parts ?

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[Cloud9...68]

the body of the IVC has an O ring under the metal top cover, mine was in a pile of bits with a massive air leak, a full clean of the ICV take it to bits replace the O ring and has now been fine for 7 years,

the ICV is the same as a Hyundai Lantra 2.0 and is considerable less money, worth a $40 experiment,

 

especially as the correct ICV is now NLA 944.606.161.01, Part dropped from Porsche stock on the 1st of May 2021, and before it was dropped it cost $400

 

I removed my ICV, and am not seeing anything that resembles what you're describing, nor am I seeing any way to take the ICV apart.  Here are some pictures of mine:

 

       

 

Could you please point out where the o-ring you replaced is located?

 

Also, I found one on eBay for $39.95:

 

NEW Idle Air Control Valve FOR Porsche 968 1992 1993 1994 1995 | eBay

 

No idea if it's any good, but you could buy and replace a lot of these for the price of a Porsche original, if it were available.

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[Waylander]

Ok so the join between the steel top and the ally body, there are three fold over tabs, you have to bend these tabs just enough to clear the alloy body and gently remove the top part, the o ring is between the alloy and steel around the top of the alloy body in a groove



And I would snap that spare one up sharpish,

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[Cloud9...68]

I was wondering about that, but it doesn't look like the kind of thing that wants to be taken apart.  Thanks for confirming;  I'm very interested to see what I will find.  In general, for whatever reason (maybe because my car has never lived near the coast, and has always been garaged, as far as I know), whenever I inspect parts that are usually neglected, they tend to be in great condition.  Hoping to see a disintegrating o-ring inside my ICV, as that would be the smoking gun I'm looking for with this erratic idle problem.  Thanks for your advice.

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[Cloud9...68]

Well, I managed to take my ICV apart, and much to my disappointment, this 30-year-old o-ring looks like it was installed yesterday:

 

   

 

   

 

Of course, just because it looks visually good doesn't necessarily mean it has shrunken enough to create a leak.  If it were you, would you go ahead and replace it with a new one, or should I look elsewhere for the cause of my idle problem?  Thanks.

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[Waylander]

While its in bits replace it



At least you can now check it moves in both directions freely



It sits at a centre point and the ECU tells it to open or close depending on the signals



So open speed up, close slow down and it does this really fast

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[Cloud9...68]

Thanks - I was also leaning toward replacing it.  I'm trying to convince myself that an o-ring like this would seal more poorly at higher ambient temperature, as my idle problem seems to be worse on hotter days.  I would think that as both the rubber and metal expand more at higher temperatures, the seal would improve, but maybe I'm thinking of it wrong.  

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