Still not sure I understand how the ECU is supposed to interpret the inputs then.
Well, the cpu has value inputs that define X when Y - not sure how to explain it. The cpu is preprogammed with certain values Y when values X match up (these are sent from the air temp, engine temp and lambda sensor). As the coolant (or any other) temp changes the raising/falling temp values tell the cpu to decrease/increasse the ammount of fuel-air mixture into the engine for better combustion.
"the temp sender sends the cpu the info"..agreed but what does it do with it?..
It reads the data and adjusts the air-fuel mixture based on preprogrammed values in the cpu (that's what engine management programm is for). It's not a cold to hot engine transition; it's a gradual increase/decrease (the same as the engine warms up or cools down gradually and not in a sec).
The "drop of rpm happens when the core warms up"...what tells the ECU this?
The coolant temp sensor that's in the thermostat (maybe there's another one, but i don't think so). The stat is basically a part of the enigne and as the coolant circulates inside the engine it goes into the thermostat and temp sensor (cold and warm water circulate because of the temp difference even if the stat is fully closed) and that's the data the temp sensor sends to the cpu and because the air-fuel mixture is too rich or too poor it has to adjust the parameters to stay in the allowed arrea (Euro norm) and to ensure proper and efficient combustion (the TS has two sparks in each head to comply to the Euro2 norms; the JTS has only 1 spark per cilinder and a couple of catalytic converters more to comply to the stricter euro3 emission norms).
The MAF (especially if it's a BOSCH model) is the most common failure of every "modern" engine that uses air measuring sensors but the diagnostics tools don't report MAF problems, because the engine is still capable of operating normaly even if the MAF is disconected. The lambda sensor, on the other hand, is noticed by the cpu engine management, because it tells the cpu at what efficiency the air-fuel mixture is burning and if it isn't working properly the mixture is way off what it's supposed to be and you can notice symptoms like rough idling, high consumption, hesitation when accelerating and it can even wear the engine. Next, the lifespan of an unheated lamdba sensor is 30.000 miles and of a heated one 80.000 miles. Not sure if the GTV has one or the other, but whereas the lambda sensor costs 50 pounds the MAF (original) is 300 (at least here in slovenia)!