Perplexed - 3.2 won't idle when cold

[wjdunham]

Originally Posted by tholyoak

Based upon the description of how the oil tank is plumbed, I don't see how it is providing a source of false air. My understanding is you have the breather hose from the case connected to the oil tank, the other connection at the tank is vented to the atmosphere to allow the case not to create a vacuum. The port on the throttle body boot that would normally connect to the tank is plugged. Thus no air leak on the intake side.

You are correct. John, maybe I wasn't clear in my initial description, the oil tank and thus the crankcase is vented to the atmosphere. The intake side is sealed up and NOT vented to the atmosphere.

Have you checked or eliminated the IAC valve as the culprit. I can imagine if it is stuck in the open state it will continuously leak air past the throttle plate and result in a lean mixture.

I can try swapping it with the one in my '85, but I assumed that once the car warms up a bit and holds an idle fine then the IAC valve is functioning properly. I guess that will be today's project to rule that out 100%

Based upon your resistance values I don't think there is anything wrong with your CHT sensor. As stated above, mucking about with resistors to simulate different engine temps is just allowing for compensation of the lean mixture you have when the DME knows the correct engine temperature.
Again, this is all based upon the idea that you have a lean mixture that cannot be compensated for within the AFM adjustment screw.

-Todd

I did try propping open the barn door a bit to richen it up, the car wouldn't even fire so it was way too rich at that point. I didn't have a lot of time, so today I will pry it open a bit less and see if I can get it going. If that works and I can get a stable idle, then I would think I'd be able to do the same by closing the screw on the AFM all the way in, but that doesn't get it rich enough. I'm hoping that the PO didn't mess with the AFM spring, but I can't rule that out.

[911obgyn]

The crankase, thus the oil tank, are under vacuum. The breather is like leaving the oil cap off. Only a bigger leak.

[prschmn]

I'd lose the Wong chip regardless.

[wjdunham]

Originally Posted by 911obgyn

The crankase, thus the oil tank, are under vacuum. The breather is like leaving the oil cap off. Only a bigger leak.

OK, light bulb moment... I did not realize there is actually a vacuum on that line coming from the oil tank to the intake. If so, then yes, I effectively have an air leak. Will plumb that up today and let you guys know how it goes.

On the SW chip, I need something other than the stock chip due to the engine configuration - 964 cams, SSI headers (I know, too small...), 3.4 with different compression, enlarged throttle body. I did consider Sal's MAF setup but that is $$$. What other options are there?

[prschmn]

Despite what's changed it's nothing radical. I have built very similar engines with just a change in injector size. The DME doesn't know the difference.

[tholyoak]

Perhaps I am being dense but this makes no sense to me.

As long as the tank is not plumbed to the intake, it is not an air leak. Based upon the way the plumbing has been described, there is not a connection between the oil tank and the intake, thus the air being drawn through the tank is only from the atmosphere and into the case (below the combustion chamber). Thus it is only a crankcase ventilation system and I cannot see how it is allowing false air into the combustion chamber.

-Todd

Originally Posted by 911obgyn

The crankase, thus the oil tank, are under vacuum. The breather is like leaving the oil cap off. Only a bigger leak.

[wjdunham]

No luck with the oil tank to intake hose :-( Same behavior as before. Tried propping open the barn door and no real change with that either.

The only way I can get it to stay running is to crack the throttle just a bit. Going to swap the known good ICV from my '85 and see how that goes.

[ant7]

Just a thought, and seen as you have tried most of what others have sugested, have you inspected the track in the AFM, ie; I wonder if the wiper is making proper contact with the start of the track ?

Originally Posted by wjdunham

No luck with the oil tank to intake hose :-( Same behavior as before. Tried propping open the barn door and no real change with that either.

The only way I can get it to stay running is to crack the throttle just a bit. Going to swap the known good ICV from my '85 and see how that goes.

[wjdunham]

Originally Posted by ant7

Just a thought, and seen as you have tried most of what others have sugested, have you inspected the track in the AFM, ie; I wonder if the wiper is making proper contact with the start of the track ?

Yes, I had already re-tracked the wiper per the methods that have been described on the forum.

[ant7]

In that case, are you absolutely sure you have no pipes disconnected from the inlet system, because if everything that has been mentioned has been checked then it doesent really make any sense.

Originally Posted by wjdunham

Yes, I had already re-tracked the wiper per the methods that have been described on the forum.

[mysocal911]

Originally Posted by wjdunham

No luck with the oil tank to intake hose :-( Same behavior as before. Tried propping open the barn door and no real change with that either.

The only way I can get it to stay running is to crack the throttle just a bit. Going to swap the known good ICV from my '85 and see how that goes.

Have you missed some posts or do not understand test procedures?
The reference in post #4 describes in detail how to check the ICV operation, why haven't you done that.
Maybe you need to consider taking the vehicle to a good Porsche repair shop at this point!

[wjdunham]

Originally Posted by mysocal911

Have you missed some posts or do not understand test procedures?
The reference in post #4 describes in detail how to check the ICV operation, why haven't you done that.
Maybe you need to consider taking the vehicle to a good Porsche repair shop at this point!

I just haven't had the time to to that test, I did read the post and fully understand how. I've been trying to eliminate all the other possibilities first. I've rebuilt this entire car bolt by bolt and so far this is the one problem I have not been able to solve on my own (with a lot of help from this forum :-)

Gratuitous photo of the car in question

[917_Langheck]

Sometimes pulling teeth actually is easier....

[wjdunham]

Originally Posted by mysocal911

Have you missed some posts or do not understand test procedures?
The reference in post #4 describes in detail how to check the ICV operation, why haven't you done that.
Maybe you need to consider taking the vehicle to a good Porsche repair shop at this point!

No need for the repair shop, problem solved. I ran the ICV test exactly as described, with the vane shut the car would not start at all, but with the vane wide open it would start and idle very high (like 2000 RPM) as expected. As soon as I plugged the harness in to the ICV the car died. Certainly looks like an ICV issue, now do I feel like a real idiot.

I pulled the known good ICV from my '85 and put in into the misbehaving car, and wouldn't you know, it holds an idle fine while cold. It was idling very high, I had to screw the idle bypass way in, as it was backed way out as a band-aid for the bad ICV to get it to hold idle even when hot. The effect of the bad ICV looks to be an overly rich condition, not enough air getting past the throttle plate.

I'm going to leave the working one in this car and go for a drive to be certain that's really the issue, but it sure looks like it. Thanks for all the help and suggestions!

[wjdunham]

Just to close this saga out - took the car out a few times this weekend and after adjusting the idle screw and backing out the AFM screw four and a half turns she starts right up and holds an idle fine. I had to screw the idle adjust in like seven or eight turns, as that was the only place air was getting past the throttle body with the bad ICV. Thanks for all the help, definitely should have checked the ICV much sooner in the process, but I had thought incorrectly that once the car was warmed up and it held idle fine that the problem could not be the ICV.

I did have one issue after the engine got good and hot, would not re-start. Let it sit for a minute or two and it did fire up fine, but I'm a bit worried there is still some issue that needs to be addressed. May be time for a wideband AFM to make sure all the adjustments are set properly.