Raised idle above 1k is normal when engine is cold.

Because of the age, if you know that's the original main relay, I might consider either re-flowing it's solder or just replacing it if I was in your position. It's not super expensive, is fairly easy to replace, and it will almost certainly need to be replaced eventually anyway. If you search around you'll find a pic or walk-through to help locate the relay, otherwise a service manual is a good thing to have.

You say you have spark, but I'm not sure if - depending on how/when you checked for it - you actually do at the times the car doesn't want to start. If I'm not mistaken that model has a distributor (not coil-over-plug w/ the indiv. coils) so it could possibly be the ignitor a.k.a. ignition module that is acting up randomly when underhood temps. are warm enough - could also be the connections on the ignitor possibly being loose or not connected properly(in your case I doubt that b/c it always starts when cold).

As for the injector issue, that might be it, not sure. You could try something that will not only clean but lube the fuel system like seafoam/lucas upper cylinder lube/marvel mystery oil. Seafoam might do more to clean, marvel more to lube. Marvel is the cheapest, lucas is good stuff but expensive. If you added MMO to the tank a few times and noticed the problem went away for example, you could lean towards an injector that was leaking, if it does absolutely nothing (entirely possible) than you're only out $4 or less for the MMO.