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It's your Crank Position Sensor (CPS). If it's original (probably) it can be a real bear to replace. Soak it in PB Blaster for a week or two before even attempting to remove the allen head bolt & pull out the sensor. Don't be surprised if the plastic bits of the sensor crumble in your hand as well. Your fuel hoses are probably original and those must be replaced or you could have a Car-B-Q in your garage. Under the intake plenum there's an Idle Stabilizer Valve (ISV) which may or may not be working properly - sounds like it isn't. There are more vacuum hoses & clamps, hard vacuum lines & rubber connectors under there than you can imagine. Be sure to replace the water bridge and oil fill gaskets (while you're in there) as it's just easier to do it all at once. Even after a top end refresh you'll want to smoke test the intake to look for vac leaks. For an 86.5 you're looking at $1K in parts, not including labor if you don't do it yourself. The deferred maintenance catches up after a while and it sounds like it's time to bit the bullet and Get-R-Done.
NOTE: Do not buy any parts from a local auto parts store or Ebay, etc. They won't fit, won't work, or will be for the wrong part for the MY car. 928s have many year to year & mid-year changes. Roger Tyson at 928sRus and Mark Anderson at 928 International can help you ensure you're getting the right parts the first time.
It's your Crank Position Sensor (CPS). If it's original (probably) it can be a real bear to replace. Soak it in PB Blaster for a week or two before even attempting to remove the allen head bolt & pull out the sensor. Don't be surprised if the plastic bits of the sensor crumble in your hand as well. Your fuel hoses are probably original and those must be replaced or you could have a Car-B-Q in your garage. Under the intake plenum there's an Idle Stabilizer Valve (ISV) which may or may not be working properly - sounds like it isn't. There are more vacuum hoses & clamps, hard vacuum lines & rubber connectors under there than you can imagine. Be sure to replace the water bridge and oil fill gaskets (while you're in there) as it's just easier to do it all at once. Even after a top end refresh you'll want to smoke test the intake to look for vac leaks. For an 86.5 you're looking at $1K in parts, not including labor if you don't do it yourself. The deferred maintenance catches up after a while and it sounds like it's time to bit the bullet and Get-R-Done.
NOTE: Do not buy any parts from a local auto parts store or Ebay, etc. They won't fit, won't work, or will be for the wrong part for the MY car. 928s have many year to year & mid-year changes. Roger Tyson at 928sRus and Mark Anderson at 928 International can help you ensure you're getting the right parts the first time.
Good Luck!
Totally get it. I am very much "while you are in there" type of mechanic and will address these. I've owned the car since 2004, and have done several belt changes and now it's time for the refresh. Thanks Jbrob007.
Totally get it. I am very much "while you are in there" type of mechanic and will address these. I've owned the car since 2004, and have done several belt changes and now it's time for the refresh. Thanks Jbrob007.
Bob
So under the intake (I assume it requires removal) is this Idle Stabilizer. Am I able to view it physically from above? Yes it is definitely not working properly. I put it into gear and it drops dead and have to restart it. Once warmed up, it seems to work OK. Arghhhh this is frustrating. It had been acting up when putting the car in park and reverse before I had the belt service. I believe the belt service triggered the starting problem, now the idle issue has been exasperated.
Mark from 928 International thought it might be under the passenger intake plenum. Thoughts?
Thanks, my problem, I am working on a car on the lift and need to have the Porsche in and out of the garage to service the car on the lift. Damn its heavy to push up my driveway solo.
If you peer between the intake parts, you can see the ISV. IF you remove them, which isn't hard, you can access it. You might bleed a little, you might curse a little, but you can access it without unbolting the manifolds. You remove the side parts, then the large middle T.
The ISV could be ok if the hoses are cracked or loose. There are lots of threads about top end refreshes and ISVs. Reading them all could keep you busy for a few nights. Examine every hose in there, and clean everything, and consider doing what people here call a "top end refresh" which replaces a pile of wear items.
If you peer between the intake parts, you can see the ISV. IF you remove them, which isn't hard, you can access it. You might bleed a little, you might curse a little, but you can access it without unbolting the manifolds. You remove the side parts, then the large middle T.
The ISV could be ok if the hoses are cracked or loose. There are lots of threads about top end refreshes and ISVs. Reading them all could keep you busy for a few nights. Examine every hose in there, and clean everything, and consider doing what people here call a "top end refresh" which replaces a pile of wear items.
Is this the ISV??? I can see it on the Passenger side. It does look weathered. The large hose going into it, that isn't coolant is it? Or a vacuum valve?
This photo does not show the idle valve itself (for some reason I don't have a photo that shows it!), but it shows Where you look to find it on the S3.
Please excuse the removed cam covers, they do NOT need to be removed for you to check the state of the hoses under your itake.
This photo shows the side plenums, the bigT, the airbox and the MAF removed. If you remove all of these, you can clean the engine V, check all the hoses under there, check all the hose clamps, and remove and inspect the ISV. It sits in the V. T
ake heed - if the rubber connectors between the plenums and the intake runners are old and stiff, you will have a hard time getting the plenums to be perfect -- and a vacuum leak at the plenums can be hard to see, but it can cause funky idle drops, and so could be your problem.
This photo does not show the idle valve itself (for some reason I don't have a photo that shows it!), but it shows Where you look to find it on the S3.
Please excuse the removed cam covers, they do NOT need to be removed for you to check the state of the hoses under your itake.
This photo shows the side plenums, the bigT, the airbox and the MAF removed. If you remove all of these, you can clean the engine V, check all the hoses under there, check all the hose clamps, and remove and inspect the ISV. It sits in the V. T
ake heed - if the rubber connectors between the plenums and the intake runners are old and stiff, you will have a hard time getting the plenums to be perfect -- and a vacuum leak at the plenums can be hard to see, but it can cause funky idle drops, and so could be your problem.
Now I see you want to have a refresh, I get it. I was just going to ask you for a photo. Thanks, is that an 86? Mine looks a bit different. The car is running, just have to warm it up well before driving. Hopefully in a couple of weeks, I can get my other project off the lift and put the Porsche on there. Limited for space in my garage. Will keep you posted.
That Red arrow is not pointing to the correct side.
The ISV is on the Drivers RIGHT side, in your picture you can see one of the rubber hoses connecting to the ISV to the Throttle body.
That Red arrow is not pointing to the correct side.
The ISV is on the Drivers RIGHT side, in your picture you can see one of the rubber hoses connecting to the ISV to the Throttle body.
Auto parts are always referenced as if you are sitting in the drivers seat, not looking at the car from the front of it.
So "Drivers Right" would be to the left of the Oil fill looking at the car from the front facing rearward.
the red arrow was just to show that in generall you reach into the V of the engine, between the intake runners - not the sides overtop the valve covers.
yes, that's an '86. It is far from perfect - note the broken hood switch, cracked cowl tray, and the utterly terrible washer fluid snorkle and cap! - but it works well. And I do have the jump post cover. Here is what it looks llike assembled.
Well ISV is out. Could not loosen the bracket screw that holds the valve, so had to remove the entire bracket from the mounting point. Well that was fum.
I applied a 9V battery to it (Positive in the middle and negative on the outer pins). Both sides nothing. I put the negative in the middle and the Positive on the outer, still nothing, no click, movement, vibration.
01-18-2023, 09:24 AM
