I'm aware that head gaskets are a common problem on Supras/SC's. (Apparently on older ES's too, but that's a different story...) Anyway, my car has, on a rare occasion, done some funny things since I've owned it, and I'm starting to wonder if maybe a head gasket is in my future. First off, since the first time I ever looked at it, I've noticed that it doesn't idle as smooth when you FIRST start it up as it does once the engine is warmed up. Another thing is that on an extremely rare basis, the idle will drop below normal until it's at about 500RPM and it feels like there's a miss. However, the split second you give it a little gas, it responds just fine, but once it idles back down, the same thing will happen. Then, next red light, back to normal...The third thing is that from time to time, with the engine warm and the A/C off, the heater will blow cold air for a while and then, for seemingly no reason (and I've tried to make some sorta connection as to what triggers it but can't really find one) turn hot and stay hot until/unless you turn the thermostat down. The last thing that really has got me thinking about this is that in the 25k miles I've owned it (now up to 155), it's gotten a little too warm twice, and I believe that I pinpointed the cause to a lack of coolant in the reserve tank. It just seems to be disappearing, but not out the overflow hose-somewhere else...I've not noticed any oil in the coolant, although it is quite dirty (I plan to flush it once the weather warms up) and no coolant or moisture buildup in the oil or on the dipstick as my dad noticed on his old Supra just before head gasket time. It also doesn't smoke or have a peculiar exhaust smell. I replaced the plugs a while back and they all looked perfectly normal, albeit a little dirty from 13 years of driving. SO, all that said, what do you guys think? Anything sound familiar? (sorry for the long post...just wanna be precise)