Did you find out your problem on this? I know I'm late with a suggestion but my guess is you were losing residual fuel pressure after shutting off the engine. In order for the engine to start in hot start conditions the system was supposed to stay within certain fuel pressure parameters within about a 30 minute window, so the instant you hit the key the injectors had a spray pattern. I'm wondering if one of the fuel pump check valves allowed the pressure to bleed down right away resulting in no fuel pressure within the time frame of 20-30 minutes or so from the moment you turned the engine off.
When you would bypass this function of the residual fuel system by manually engaging the cold start valve you kind of jump started the system. My guess is the engine ran a bit rough when first started warm using your cold start method but at least it started.

 

I have not figured this out yet. The way I left it, I was going to remove the intact air duct and inspect for cracks and any other major vacuum leaks. But I've been waiting for the weather to improve.
Someone did mention fuel pressure loss but then it was shot down when someone else pointed out it will fire right up after sitting all night. So I didn't really give it any more thought.
Is the only way to check this to hook up and measure fuel pressure? I'm guessing it is. I suppose I should buy the kit from JC Whitney that was recommended by another user.

 

Another thing I noticed is that it wont idle cold either. If I am driving it while it is cold it dies whenever I come to a stop. If I just start it and let it idle to warm up, it will die two or three times until it warms up. Then runs fine until I shut it off.
So I don't think that behavior says fuel pressure. Unless fuel pressure is handled differently from cold to warm.

 

You do want to inspect especially the bottom side of the boot from air flow sensor to throttle body, and for other vacuum leaks as that does play into how far the air flow sensor raises up to distribute fuel. If you have a split in that J boot not only does it run bad from the vacuum leak but the lack of intake air doesn't allow the air flow sensor to raise up as far as it needs to be and the height of that disc depends on air flow. The less air flow there is the less fuel gets to the injectors.

But in answer to your question yes, fuel pressure is dependant on the temperature of the engine and to a certain extent outside temps too. If all systems are working fine, the reason the engine starts quickly without issues is because the coolant temp sensor knows the engine is cold. So the cold start valve is told to squirt gas in for no more than I'd say 2 seconds and only if it's colder than let's say 55 degrees. I don't have a book in front of me so I don't know those specs. It appears yours if working fine in this area. So the warm up regulator is bolted to the block and it's temperature sensitive. It has a bimetal spring in it and as the engine heats up so does the spring inside and as the engine warms up the fuel pressure goes from a lower pressure to a higher pressure applied to the fuel head mounted on top of the air flow sensor. That fuel head on top of the air box is fed fuel to the center area then distributed to the injectors via ports inside of it. The heart of the system is the warm up regulator. That is what changes the fuel pressure from low pressure when cold to higher pressure when warm. The air flow sensor has an arm with a disc attached to it that senses air flow from the engine via rpm and how far open the throttle body is. If there is very little fuel pressure acting on top of the air flow sensor arm then the arm is allowed to move farther up in its travel and this allows for more fuel flow to the injectors. Then as the engine warms up the warm up regulator changes fuel pressure to a higher value, this leans out the mixture in a primitive method by forcing more fuel pressure to the fuel head and this now makes it harder for the disc on the air flow sensor to raise up at that same given rpm and throttle body opening angle. So now the fuel system is running leaner just because the fuel pressure has been raised by the warm up regulator.

I did find some specs on your car for fuel pressures, and you need a fuel pressure gauge that is able to tell you fuel system and control system pressures. Or, cold and normal operating system pressures. System operating pressure the gauge should read 85-95 psi and you would want to test flow also which is supposed to be 760cc's at 30 seconds. Where I think your problem could be is in the systems inability to hold pressure after then engine has been running and warmed up and then turned off. The system should maintain and hold a minumum of 49 psi for 10 minutes after shutting off the warm engine. If it goes to far less than that or nothing that explains why you need to engage the cold start valve to jump start the fuel system so to speak. I don't have very good specs on various cars, I googled and used tech sheets that napa auto parts puts out so I am mainly wanting to give you an idea of how the system works and quoted specs to give you an idea how pressures change the mixture. You should get yourself a book on your car and then this would all make better sense.

The o rings at the injectors could be a vacuum leak too. Pop those out and replace, and check your spray pattern while you are at it.

 

So I have been putting up with my car running less than desirable for the past couple months because I couldn't figure out what is going on....but it was still drive-able and got me to work and back.
Well yesterday, after sitting for a week, the issue has gotten considerably worse. I was hoping the new symptoms might spark some new suggestions.
Now it wont start at all. I have to hold down my cold start valve over-ride switch that I installed for quite a long time and then fire it up. And I have to keep it revved up to 3k or 4k RPM for a minute or two. I have to do this a couple times before I can let it rev down to 1k rpm and put it in gear. It will not idle now either. Never. Not when it's cold, not after it's warmed up, not when I'm rolling down the highway. It's become very tricky to get around in the thing.
So does that give anyone some new thoughts on what's going on here?
I'm about to put a for sale sign on it if I can't get this fixed soon.