@Schulisco, true; because the corrosion didn't move when I swapped the injector lines, that makes me think that the corrosion must be in the injector or the line, not the fuel distributor. For example, when I started testing, fuel coming out of injector #2 was darker than the rest. I then moved the fuel line going to cylinder #2 from its position on the fuel distributor to position #3; the corrosion stayed at cylinder #2 even though it was getting fuel from cylinder #3's old position on the fuel distributor.

Does that conclusion make sense, or am I missing something?

With new injector seals installed, I sprayed a little starting fluid on the injector seats; the engine revved up every time I did. That leads me to think that the seals around the injector inserts are bad. The Bentley manual says that injector inserts can be removed using a hex key, but mine don't appear to have a hex pattern. I did a little YouTube research, and it seems like my inserts may have to be removed with the intake runner removed. Anyone have any bright ideas that don't involve pulling intake runners?

AAV and AAR test good. Sprayed the decel valve with starter fluid and the engine revved. Air hoses look good, so thinking that valve has failed. Should pull off car and bench test with a vacuum.

The injector sleeves/inserts are held in place by staking the edges of the intake runner around the sleeves. Look closely and you will see where the aluminum was staked around the sleeve. you have to grind or file the edges to "unstake" the sleeves. Then re-stake them when you put in the new sleeves.

I think you are at a decision point. Do you want to get the car running good enough to drive through the summer, then pull the CIS off and pull it apart and renew things as necessary in the winter, or do you want to do it now? To replace the injector sleeves and the O-rings at the bottom of the sleeves, you will need to remove the CIS from the engine. It's a PITA, but you can do it without dropping the engine.

"switching fuel lines between 1 & 2 and 3 & 4, but the discoloration stayed at 2 & 3 both times"

By that, I assumed the OP swapped lines and the contamination stayed with the injectors, that's the way I read it anyway.

Update! After my mechanic (3R Racing/Performance) replaced the fuel injectors and the fuel injector sleeves, the low engine speed response and smoothness improved drastically. No more chugging at 1,200 RPM in first or second, much smoother.

The cold start didn't change at all, however, and the idle speed went down a lot. So, more vacuum leaks to find and more CIS gremlins to defeat.

The revs seem to drop more rapidly than they used to. I think I'm going to test the rev hang valve first.

Didn't answer yet.
Whenever there's corrosion in the system, you can to expect it everywhere. If you're lucky only single components are affected. The fuel lines are made of steel (afaik no stainless steel) but they won't corrode that quick and much as many other components.

Good progress!

Cold start is mostly affected by mixture/amount of fuel delivered (and therefore system & control pressure), constant fuel delivery (fuel accumulator & check valve), correct ignition timing and tightness of the CIS system.

These are the effects I mentioned earlier. The behaviour of the system after resolving some issues might by controversal against expected as still some issues persist.

The reason for the quicker drop of revs is that less air is available as some leaks have been sorted out. So this quick drop should lead to check the AAV for correct function. Also check the mixture now, I expect it a bit richer now. Also check the injection begin / basic setup of CIS as I mentioned earlier in #12.

Thomas

Update: after an expensive but worth it service bill from 3R Racing/Performance, the source of the cold start trouble has been located. My car, a 1977 911S 2.7 sold in California, did not have a check valve at the fuel pump installed from the factory. For that reason, the long fuel line from the pump to the engine bay was down on pressure for every cold start.

Since a check valve was installed, the engine fires immediately upon cranking from cold. If you're having cold start problems, check to see whether your car has a check valve at the fuel pump at all!

Performance and driving characteristics have improved vastly since a huge number of vacuum leaks were rectified with new rubber. The car runs so well now: no idle hunting, no excessive rev hang, but no huge drop either, great warmup characteristics.

Notably, the car is much more eager off the line as I let out the clutch. Before, it wanted to die the moment I'd let out any clutch and I'd have to give it a lot of revs. I learned to drive stick on this car, and I thought I was going crazy because I would stall it all the time. Now, with no vacuum leaks and no stumble when I let the clutch out, it's as smooth as butter!

Good to hear you got it fixed.

Somewhere in the past few months of testing you should have run a specific "residual pressure" test. That would have showed that you were losing RP too quickly, and led you to the check valve and/or FA. Since I just looked back briefly, I didn't see the time for the RP leakdown. Did you do that and what was the result? If you still haven't done that, do it now anyway. I'm not just rapping your knuckles--the FA may be leaking too if you didn't already replace it.

Pete,

Good call; I haven't been doing any of the work on the car since June, but I am not sure if my shop did a residual pressure test. I could do one in a couple weeks, that would be good.

The FA is 1 year old, it's an upgraded unit from an SC. I would be surprised if it had gone bad, but not impossible for sure.

If you replaced the FA a year ago, it should have plenty of life left. Still do the RP test to be sure it holds RP for at least 30 minutes, preferably a lot longer.

I have a 77s Targa which can be difficult to start. If it's cold (winter conditions) it fires up relatively easy -although not necessarily on the first crank.
However in warmer conditions from cold it can take about 20 secs of cranking and eventually it splutters into life.
Once started the car runs well and if it stalls will start immediately.
Looking for pointers as to where to start looking please - fuel pressure ?

James,

You need a pressure tester kit to check your fuel pressures (control, system, & residual). Then confirm your CSV (cold start valve) and TTS (thermotime switch) are both good and working. Make sure you don’t have a significant amount of unmetered going into the system. And you’ll be able to start and run a CIS motor. Good luck.

Tony