Headstuds? yes, check them. The 3.0l SC's unless the 83 is somehow different are all dilivar.

As far as your first point, it's true, my EFI has never died, or left me stranded. If you have a starting issue, hot or cold you can just plug in and see what the issue is, adjust and move on.

Paul - forgive my ignorance. Are you saying that the lamda brain affects running conditions even when the O2 sensor is disconnected?
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mca,

Yes, the lambda system uses a pulsed injector (FV) as a variable restrictor to manipulate the lower chamber fuel pressure in the fuel distributor. All closed loop systems have to dither the mixture back and forth around 14.7:1 for the benefit of the cat. The default setting for the SC lambda is in the middle, 55, and if there is no power to the lambda brain, or pulse to the FV, it stays closed. The engine runs poorly because the basic CIS settings are too lean without the FV pulsing in the middle of the range and controling the lower chamber pressure. When the FV's duty cycle is high, chamber pressure goes down and the mixture get richer. Low duty cycle means the basic mixture is rich and the system is correcting to stoich by raising the pressure and leaning the mixture. . You can see all this happening with a simple dwell meter, like you use to tune up your 64 Vette, and it is very nice in a pre OBDII way. You can hear the FV buzzing if you know what to listen for, the first suspect should be the relay.

Paul

So what you are saying is even if the o2 sensor was unplugged it would still run but if the relay goes out and it's not getting power the car won't run very well? And now that you said that about the buzzing I don't remember hearing now that it won't run but I could hear it before. One more thing on my list to check later today.

Intake popping suggests a lean mixture, or an exhaust leak, which also causes a lean mixture. Exhaust popping is generally an exhaust gasket leak, allowing air into that hot exhaust manifold, igniting unburned fuel.

CIS malfunctions should be determined by following the standard CIS troubleshooting procedures.

I just checked the relay under the seat and it seemed not to be working I replaced it and now it clicks on and off and is getting power however I still hear no buzzing like it should and it doesn't change anything when I unplug it while the car is running. Any ideas?

If you've got an '83 SC, a ROW one, that still has the stock CIS system, and if unplugging the small "ice cube" relay under the seat does nothing to change how the engine runs.......then you found the problem. Regardless of whether your O2 sensor is plugged in or not, that relay HAS to be operating and the Frequency Valve HAS to be operating, in order for the engine to run properly. Unplugging that relay MUST cause the engine to suddenly run poorly. If not, then that system is already not working, and it must work.

So now I tried unplugging the Frequency Valve and nothing happens, unplug the o2 control unit nothing. Anyway of testing the FV in the car? or maybe the control unit is bad? I think I've narrowed down the problem now all I need to do is find the solution to it.
Does the FV run off 12v or resistance to ground?
Any ideas?

It uses switched grounds, it's powered directly off the relay under the seat, the lambda computer then switches it's ground.

So if the FV is getting 12v on one side and the ground is not working the control unit is bad?
I checked the pins on the control unit I'm only getting constant power to one pin and thats it nothing comes on with the key. The relay I replaced to old with is different it clicks on and off but could that still not be allowing power to the control unit?

I also connected a old injector to the FV plug and nothing happens no click nothing so I think the FV is good maybe the relay or control unit. I work right by an Audi store so I'll try to pick up the right relay in the morning to see if that helps.

Best thing to do is to find another Pelican in your area that will allow you to use their computer for testing. Maybe you could borrow one from a p-car wrench in your area as well.

I had a few issues with my first lambda brain and it turned out to be bad solder traces at the block connector, pretty easy fix really.

I found that on mine, the relay clicked but was still no good. Check power in and for power out when it clicks.

I'd read somewhere you can use the control unit out of older vw's and audi's and it will run the FV and the car will run better but not have the right maps and cold start?
Anyway I'm going to pickup a new relay just to make sure I've got the right one and then I'll go from there.
And thanks to everyone for their help thus far and hopefully I'll have it running by this weekend.

Just an update on the car. I went to Audi at lunch no relay in stock so I just got home and went to check make sure the relay I replaced it with is working the same way as the old and sure enough no power on one prong. So I ran a jumper wire and the right when I plugged it in there was that sweet sound of a humming FV, started up ran perfect maybe not perfect but as good as before.
So thanks to everyone for all their help and I'm sure I'll have other problems I'll need help with.
Thanks again Lee

Why are you selling the SC lee?