My car decides when it wants to start

[carfanatic89]

I have a 1987 supra NA with a manual trans. Ok well about a month ago my car started acting up, it wounldnt idle and wouldnt start. I found out that oil was on the top of the spark plugs, pulled the intake off replaced the valve cover gaskets and the 4 plugs in the middle of the head i put silicone around them. After working on it, it would only start when it was cold and run fine but if you kill it when its warm and try to start it again it will not you have to wait till it cool again. And now recently it just runs when it wants to. It will start, rev to about 1700 rpms then slowly rev back till it dies. I put in a new coil, spark plugs, and O2 sensor, but with a small budget I dont want to keep throwing parts at hoping it will fix it. Has this kinda thing happened to someone else. Can someone give me a guess on what it is. oh and the exguast smells bad and doesnt smell like gas or burning oil and it doesnt smoke. I also ran a diagnosis and it told me air intake temp. sensor (dont know what that is), netural switch (it turns over but wont start), O2 sensor (just replaced that a month ago) Sorry for the long post.