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Hmmm, what size fuse is installed for the "EFI" fuse in the same fusebox. The EFI fuse should be a 15 amp fuse and I'm wondering if someone may have installed a fuse with a higher rating. Check the rating of the "IGN" fuse as well. Should be 7.5 amp fuse. The fact that replacing the EFI relay with a new relay temporarily fixes the problem leads me to think that something is drawing excess current through that relay and damaging it with time.
Try shorting the fuel pump check connector and turn the ignition switch On. Then let the fuel pump run for a couple of minutes and see if the EFI relay gets hot . Let me/us know what you find with this test.
 

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I forgot to ask which car is having this problem, your 82 or 85? The measurement of 0.3 ohms on the ignition coil would be for the primary winding. Check the secondary winding resistance and see what your meter reads. The reading should be 8.5 - 11.5K ohms on the secondary. Page IG-6 in the 85 TSRM. The EFI relay no. 2 feeds the ignition coil primary, the igniter, the injector resistor pack, and the fuel injectors. The relay contacts on the no. 2 EFI relay are overcurrent protected by a fusible link and not a fuse so it is possible that your ignition coil could be crapping out when the underhood temps. go up. The ignition coil on both cars I believe have built-in thermal overload protection which would explain the erratic tach. needle movement and the ability to restart after things cool down. If the coil draws too much current, the no.2 relay will get hot and the thermal overload protector in the coil will open causing the engine to just up and quit. Chances are that both the relay and the ignition coil windings are cooling down during the off period, but the coil could very well be the actual source of the problem!
HTH!
 
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