If you need help with sorting out the DME this fellow (Jose, IIRC) is an expert and will take the time to help you figure it out. He helped me resolve a misfire that had stumped a small flock of mechanics. Good luck.

http://www.ecudoctors.com/porsche_process.html

Hi Folks,

So I went over to a fellow pelican's house today (Mark '87 930) and he was good enough to help me adjust my fuel mixture using the the idle mixture screw under the Air Flow Sensor. We couldn't get the LM1 probe into the bung I had welded in unfortunately, so we had to stuff it up the muffler. I believe this may give a bit of a lean reading however it was the best we could do.

Anyway, when we started up the car it was reading around 11.6 at idele (super rich), which would explain the subdipping issue. We turned out the screw but I was only able to get the AFR reading to 13.5-13.6. It got to a point where turning it didn't seem to move it any further. Is there any reason for this?

When we took the oil cap off, you could feel there was a good vacum on the oil tank, and then the mixture leaned out to 15+. We also tried to run a propane torch by the intakes and it showed no noticeable change.

Also, when I drove the car it no longer subdipped, it would drop to 600 and back to 800 but no where near the issue I was having before. I will say though that the car seemed to lack a bit of the power that I was used to. Why would this be, as I thought that the mixture adjustment only affected the idle, not the entire throttle band.

I am open to all suggestions.

The only sensor gone bad that would cause the mixture to run super rich is the cylinder head temp sensor. Try unplugging it and see of it makes a difference. If good, it should kill the engine.

I will do this, however I have done this in the past. It made the car pour out smoke and made the engine stall. I don't think it is the CHT. I was surprised because I could drive the car previously, the only problem was the subdipping. So even though the numbers appear that they were very rich, it didn't show sever rich conditions. Hence my confusion. The car almost feels like it is running lean now, with a bit of lack of power. After some reading, I am wondering if my next thing to check should be the fuel pressure. How do I do this and what kind of numbers should I be looking for?

Dennis,

In post 28, you described a stuck ICV exactly! Basically, the idle gets too high for the DME and ICV to adjust, so the DME cuts the power, the idle drops, and the DME restores power! Again and again!

This sounds like it is caused by 1 of two things:
1. Your ICV is stuck open too much, creating the symptoms above.
2. There is someting artificially raising your rpm (Air leak in the hoses from the ICV to the air flow meter, others?) and the DME closes the ICV all the way, and it can't lower the rpm enough, so the surging condition you described.

My thought, if there was enough of a air leak for condition 2, you would have found it by now. I feel condition 1 is your problem.

Good luck!

Hi Techman,

Yes, I have added on to this thread along the way and had a few compounded issues. I started out with a vacuum leak, and a DME issue which caused hunting in the idle. I have since solved those issues. I have now moved on to trying to fix a subdipping idle which is typically caused by a rich mixture. When we used the LM1 my mixture was very rich (11.5 AFR). By adjusting the AFM mixture screw I could get the mixture to 13.5 AFR. Per Steve Wong and others recommendations the AFR at idle should be 14.2-14.7. This means I am still runinng slighly rich even with the AFM bypass gate open all the way. Not sure what to check next?

I believe my ICV is working properly. When I jumper the B-C test connection which centers the ICV I can hear a noticable change in the RPM's. In the past I have also swapped out my ICV with a known good ICV with no noticeable differenc.

Slightly rich. Hmm. I usually try the 50/50 rule to help. What is that?

Split the causes in half. Broken, or being told to do that? Too much fuel. In your case, look at the DME. Is it performing properly, or improperly? Ok, say it is performing properly, and think of all the parameters that would tell it to go rich. Signal saying more air than is actually going in? What about the switch on the DME that changes the settings? If all it's input is correct, is it putting out the correct signal to the injectors? If you don't have a machine to verify, maybe swap a DME in to verify.
Next, Fuel pressure, too high? If so, try 50/50 What controls the pressure regulator? it may be broken, or getting the wrong signals. Just because something appears to be operating incorrectly does not mean it is broken. Make sure all ot it's input is correct.

Again, good luck!!

Slightly rich. Hmm. I usually try the 50/50 rule to help. What is that?

Split the causes in half. Broken, or being told to do that? Too much fuel. In your case, look at the DME. Is it performing properly, or improperly? Ok, say it is performing properly, and think of all the parameters that would tell it to go rich. Signal saying more air than is actually going in? What about the switch on the DME that changes the settings? If all it's input is correct, is it putting out the correct signal to the injectors? If you don't have a machine to verify, maybe swap a DME in to verify.
Next, Fuel pressure, too high? If so, try 50/50 What controls the pressure regulator? it may be broken, or getting the wrong signals. Just because something appears to be operating incorrectly does not mean it is broken. Make sure all ot it's input is correct.

Again, good luck!!

Thanks Techman,

I am borrowing a LM-1 this weekend. I am going to try and swap out with a known good DME, and then also check the reading with the fuel pressure vacuum line connected/disconnected. I will also reverify my fuel setting postion, which I believe is at default 0.

I will report back what I find.

I'm experiencing the same problem at start up (cold only) the engine will die as soon as I take my foot of the accelerator or come to a stop. After about a minute or two all is good.
I've read the threads and linked threads and I have a rather noob question here.
Where exactly is the AFM mixture adjustment screw?
I know where the idles screw is, but can see/find the AFM mixture adjustment screw.

Can someone post a picture of it's location?

Thank you.

You can take a look at this from Steve Wong's site.

http://www.911chips.com/C1INSTR.pdf

I believe it has instructions for adjusting the idle mixture, with a picture of the screw underneath the AFM.

Thanks for the diagram....but I think I'm missing something here.

Are you talking about the washer under the AFM front left corner?
Other than that I see the microswitch and idle screw....
No mention of the AFM mixture adjustment screw.

I thought I would close out this thread, to help any others in the future. After a pretty exhaustive effort to track down the issue, it looks like the culprit of my rich running condition was a modified FPR. I didn't even think this was possible until I saw this link on SW site.
911Chips.com - Fuel System

Anyway, a new FPR fixed the fuel pressures, and an fuel injector cleaning revealed one faulty leaking injector which was replaced. The car now runs perfectly.

I've been experiencing random ones myself, usually when I shift into neutral and begin to brake at a light it starts to surge from 1200 to 1800. Other times the throttle just gets stuck at 1800 rpm. The car has been idling at 1200.

I changed the 02 sensor and tightened the idle adjustment screw. It did not drop to 800 rpm until the idle adjustment screw was turned all the way (didn't feel like it could go any further). I loosened it slightly (didn't seem like it should be that tight) and went for a short drive. The idle returned to 1200 rpm.

Next I'll clean the idle control valve and throttle body, but what else can you suggest?

Your idle switch is not working or intermittent. That is either from it not being correctly adjusted away from the activating cam, or your throttle linkage is too tight, or the switch is sticky. Turning the idle speed screw down is only masking the problem. When the switch doesn't work, the car stays in part throttle mode, and the ECU thinks your foot is still on the throttle. See below on how to check and fix/adjust your idle switch:

http://forums.pelicanparts.com/uploa...1450570566.jpg

Valve adjustment can solve surging.

Thank you, I will give this a shot. I've also been wondering if it is the fault of the old Autothority chip. When I bought the car a year ago the PPI mechanic said the car ran rich, mentioned an occasional hunting issue but never bothered to tell me 1200 rpm wasn't normal. I'll have to send him an email to see if he adjusted the idle screw initially to deal with the richness caused by the chip or if the car was running rich despite the 1200 rpm idle... Then again I've read a 1200 rpm idle is what happens when the switch goes bad so I may have more than one problem here.

All I know is I'm in over my head, my old Jeep is so much easier :rolleyes:

Thanks again!

I didn't read all the replies, but have you checked the alternator? I had idle problems for a long time and finally discovered the alternator was bad. Because the car was on a battery tender, it never occurred to me that it could be voltage related. Just my $.02 and easy to check.

The microswitch is on all the time. So where does one get a idle microswitch? 911-606-013-00-M100 here on Pelican says it might not fit, and I found another thread that suggested it might be for the Turbo and won't fit the Carrera...

Well this might be it: 1988 Porsche 911 Carrera Coupe - Intake System - Page 3

part: 911-606-013-03-M100


Goodness that is expensive...