94 civic si B18a1. I've searched, and tried the suggestions others with similar problems have had. The rest had no conclusion or weren't quite the same problem.

First crank up when cold: Turns over fine but seems to take a good 10 secs before it seems to start. (50% chance it does)
2nd: Starts up within 3 seconds or so. revs up with the cold idle like normal. after the few 1500ish rpms for about 20secs it starts to drop like normal.... but doesn't catch and shuts down.
3rd: same as 2nd.

holding the throttle lightly keeps it running but it still rises and falls (not similar to a vacuum leak). After it warms up a bit (just enough to make the gauge even move a hair) with light throttle, It will idle on it's own somewhat decently, though still not smooth as it should and has before this problem.
When fully warm it idles with no complaints and beautifully.
Car currently isn't legal to drive yet so not sure if it drives right when fully warm or if it would lack power or stall between shifts etc.

Have checked: Plugs, wires, coil, ECM, ECU, FITV, IACV, Main Relay, TPS, Gas(sat for over a year, drained and added fresh) Intake manifold gaskets and TB gaskets (starting fluid around edges method) Cam Timing, Ignition timing (with light seemed good), Grounds at the frame and thermostat, I'm sure there's some stuff I'm forgetting.

Not sure where to go from here. Need this done as soon as possible being how my only other transportation is a motorcycle, and that's not too great in weather and winter hehe.
If I'm missing any info you may need to assist or any other questions related I have no problem supplying any info I can get or have.

Hopefully we can get this done...

 

Up for any ideas that make sense.

 

Changed fuel filter and ECT sensor. It wasn't throwing a code or anything but have read it can be bad and sometimes not throw one. This seemed to make a difference... but only as to the time it takes before the idle is stable (smooths out much sooner than before).

Still won't ever want to start the first attempt, 2nd starts much easier than before, cold idles the same and when it drops, it now doesn't shut off but seems like its barely holding the idle. goes back up as the ECU adjusts and back down about 3 times before it stabilizes and runs fairly normal

On a test drive through the alley here, incredibly sluggish while cold even when the idle has been stable. Runs like a champ after warmed up fully. Rarely some hesitation when under 2500rpm but worth the note here.

 

I'm not sure if you check the PC valve. Sometimes when it goes bad the car can act weird sometimes.. I'm not sure just my opnioion..

 

Finally a response! Haven't checked that. It's cheap enough Ill grab another and post back. Wouldn't have suspected it. Thanks!

 

try opening up the idle screw a little bit or alot and see if the problem persists.

 

PCV valve changed and no effect. Idle screw no effect as well. In addition though. I warmed it up and took it for a test drive again. May be a separate problem or help with the current one but the engine completely warmed up passed the fan kicking on 2+ cycles, everything seems great until 3800-4000rpm. Im going to try a separate post for this problem as It didnt seem to happen on the last test run but adding here as well in case it may be related.
Car runs really good (more so I think than before any of the first problem existed) but as if on a switch it loses noticeable power at 3800-4000 instantly to the point that second gear puts me forward a bit when it lets go. it doesn't bog down or lose rpm or any of that. runs smooth, just seems to drop 30hp on a switch. almost the opposite as it would do on a beefy DOHC vtec motor. Any thoughts on that having something to do with it? or what would separately cause this as well?

 

Sounds to me like you are running too cold of a plug or your plug gap is way too tight. I had this exact problem when I had a NGK 9 plug in my turbo car. I threw in some 7 plugs and it immediately went away.

You may also want to check your Fast Idle Thermo Valve on the throttle body. It's on the bottom of the TB where the coolant lines connect. The little valve in there can come loose so you may need to take off the cover and screw it back in.