Just check out the sparks at night. Helps eliminate that variable. Not saying it's your problem.

I have had an arc from the fat wire to one of the primary terminals on the coil. It happened when the car was at WOT vs. cruising RPM, though. I don't understand this as it seemed like there was more spark plug juice at higher RPM. Don't know how this can happen. Maybe, simple vibration?

You will find it with help here. Just keep volleying back info when folks suggest things.

Not to hijack, but I have never done this in real darkness, so I tried it tonight (although only at idle). Mine looked fine, but some of the plug wires glowed when I touched them. Didn't feel any juice, but it was cool looking.

Back to the problem at hand … no box under seat means no Lambda, right? That blowing interior light fuse still bothers me a bit since on US cars, that fuse powers the Lamda stuff.

If an engine has no cat, it will not have an O2 sensor, thus it also won't have the control unit for an O2 sensor.

The blown fuse has nothing to do with it.

Like I said early on, it sounds like a lean misfire. As Bob pointed out, that can be caused by a dirty injector that has less output than the rest. When you measure the CO (assuming that is done correctly) you are measuring the average of all 6 cylinders. You can have a CO number that is withing range but still have a problem, if not all 6 cylinders are firing equally.

When he reported that the AFR was a certain amount, that was a red flag because Porsche never specified the AFR as a tuning measurement. You can convert that to a CO %, and that AFR isn't far off the range of CO that is correct for that engine, but why not report the CO, if that's what we are supposed to use for tuning?

My advice was to have the CO measured, using the correct machine and procedure. The tech books tell what the ideal number is for each CIS engine and gives any specific instructions for testing (like disconnecting the hose from the air pump first, etc.) for each particular engine type. You might test different engine versions in slightly different ways.

Assuming the fuel pressures are correct, as he alluded to earlier on, it would be a good idea to check the injector flows. It's somewhat a given to make sure the ignition system is in good order, before doing all of this. I would certainly inspect the distributor, as many people don't do any maintenance to the distributor on cars that don't have points, like an SC.

JR

Luminous plasma (thank you Wiki) created in the air from the strong electrical field.

It is eerie but I don't think detrimental.

there are a lot of "if's" here in my reply.

i think it has been determined that you do not have lambda. if that is the case then you do not have the 090 WUR. IF you have the 089 then the pressures are 3.0bar with no vacuum to the WUR and 3.6bar wiht vacuum.
so IF the pressure was checked with the engine running the pressure is too low. IF it was not running the pressure is correct but also needs to be checked with it running.
i doubt this is your problem.

i would look at timing and advance along with air leaks.
check all the intake bolts. they can come lose.
injector seals can leak and are easy to replace.
since it feels like a miss like on one cylinder i would look for leaks at individual cyclinders along with plug wires.

if you do have an air leak and he adjusted the mixture ne is just covering it up.

13.6 is OK as long as it does not surge at idle or the RPM's dont dip donw when you let off the gas. since i can set mixture me personally i would richen it just to see what it does.

just because a plug wire does not arc and spark does not mean its good. you can also check resistance of each wire.

13.6 is already on the high side of his spec, give or take, so richening it up further might just mask the underlying problem.

Checking for air leaks is always a good idea, thanks for bringing that up.

JR

+1

Vacuum advance does it's primary work at lowish-mid range RPM. Cruising speed.

Your timing may be retarded if the advance pod on the distributor is not working. (part of the check distributor as suggested by JR).

Pop the cap. Hook a hose to the pod port and suck on the hose or use a mityVac and look for movement (or even listen for movement) of parts in the distributor. No movement, no vacuum advance.

All good dialogue, thanks gents. I will list these items and work through them myself and revert to the pro's if I fall short of talent / equipment. Fatal mistake I made was assuming I had a frequency valve on the car......give a boy a man's job and all.....

Hi,SmileWavy

I am a new owner of 1983 911 SC 3.0. I just bought this car last month from other States and I have to get it smog and pass the California vehicle inspection within 2 months.

I notices that it is missing frequency valve relay that located next the Lumbda control box but the car start with up with a strong smile of gas. After it warm up the idle did not really come down. I don't think I can get it to pass smog check so, I bought a new Bosch relay and oxygen sensor to replace it. After I've replaced the relay and oxygen sensor the car will start right up and get about 1600 rpm(cold engine) then 1200 rpm( warm engine) I can not really adjust idle down because when I turn it down the idle stay the same . However, if I remove the frequency valve relay the rpm will not change but when I plug it back the idle will drop down to 300 rpm-400 rpm then dies. I used propane to check for vacuum leaks and found nothing. I also check auxiliary air regulator and it seem to be work find with 27.5 ohms. If I keep the engine running with frequency valve relay plug the engine will run very nicely but after it warmed about 2-3 minutes it will suddenly dies. I can get it start again but a little difficult and the idle will be very low about 400 rpm -500 rpm then dies.

I could not find any answer that match my problem because most of the problem is cold start issue. Can anyone give me some suggestion?

Thank,

Ken SmileWavy