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I have the same issue/symptoms with my -87 745T. Check anything that change with temperature.
What I would start with is to check if there are any leaks around the injectors, I've heard of carbcleaner or WD-40 sealing the leaks temporary, if the idle changes, that could be it. The same goes for the intake manifold gasket, it would only suck air if the engine has a vaccum, when you step on it, the Turbo would push more air in and the leaks would not be noticed. When the engine is cold, you have more fuel in general and the injectors have a slight crossflow, one missfiering injector would not make too much of a difference.
Second I would check the O2 sensor, if the signal is eratic when it is warmed up, that would goof up the mixture. When the engine is cold, I belive that the ECU enriches the mixture artificially, when the engine has warmed up, it relies on the O2 sensor.
Third I would check the spraypatterns of the injectors, if the missfire sounds rythmic and has a pace to it, it could be that one/more injectors are not fiering properly. My Z-car does the missing thing too, and it started after I replaced a leaky injector with a used one.
Also check the standard stuff, like plugs, wires, cap and rotor.
Good luck, I will be changing the intake manifold gasked next, could not find any difference with the Wd40 test, but I have a gasket laying arount anyhow.
Merry X-mas, or whatever floods your boat.
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