It's been a long time since I've been here--learned a lot and was able to maintain the little S40 that could for all these years, mostly with this community's and Matthew's help. But now she's gotten really contrary--she starts OK, though a little rough, will idle, smooths out when revving over about 1800, but as soon as she reaches normal operating temp, she just dies and won't restart until cooled off to ambient (@60-70F) again.

All dash lights and the radio work and she will crank, but won't fire during the cool down period, so the issue doesn't appear to be electrical and I can hear the fuel pump priming each time the key is turned on.

I put a meter on the ECT sensor and got a good ohm reading for it cold, but haven't been able to check it while hot. Thinking it's almost got to be the ECT, but the fan isn't kicking on and running after the engine dies (fan ran @6 mins when I unplugged the ECT, I guess the ECU side is working as designed), so that has me a little mystified. Also temp gauge is behaving normally. Would appreciate anyone's experience/expertise on this before I throw more parts at her in the dark. Thanks in advance and happy holidays to all!

P.S., cleaned the MAF and that did seem to smooth her out a little, but no effect on the dying at operating temp issue.