When our d24 did similar things, 240 ended up at mechanic who said it had a bad thermostat (opening `late`/ or not at all) Car never overheated dangerously but was running with gauge showing higher than optimum+ some power loss. No issues at idling...He suggested replacing the radiator too so I never really got to know which one of these caused a real issue. Things are connected there.
After warmed up (or being hot already) `tired d24s` dont/cant/wont start up nicely if compression is not proper (but that does not happen suddenly but slowly developing) We had that too before engine overhaul (long story,rings broke,etc,bad type of oil,bad plugs,tap water,other *stupid* sh.t! and such abuse)
I hope you figure it out asap! As meteorologists say it in the Summer: ``Temperature kills!`` ...
Here`s an old school photo from the early 90`s.