You've checked all the obvious stuff. You're guess is likely right, the injectors. Very likely a bad radio noise supression relay (power stage relay) that runs the injectors. Located under the hood, I forget the precise location in 240s, but it should be clipped to a rail, left side, forward on a fender, possibly hidden a bit by a wiring harness. P/N you're looking for is 1323592, it's a multi-purpose relay, fairly common and easy to get. If you had an electric fan there'd be two of them, usually side by each, that you could temporarily try swapping for test purposes. There's more on it in the 700/900 FAQ here. Someone like Art may know if re-soldering the relay may help, I haven't bothered to research that for you. An older relay may have fairly pitted contacts, so maybe not a bad idea to replace it.

You can confirm that from the diagnostic connector, port 2, using test mode 3 (OBD DTM 3). That test cycles through a number of steps. One step is pulsing the injectors for a few seconds. Another is exercising the IAC valve, it will go tic-toc. It keeps cycling through the steps until stopped. You can hear/feel the injectors ticking, check each one. Be sure to check it when you've got a definite no start condition so you can catch it in the act.
The procedure is here in the 700/900 FAQ.
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm#FuelInjectionandIgnitionDiagnosticCodesi
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now