RPM surging, rough shifting, overheating

[89Vette]

Seems intake manifold gaskets would be a good thing to look at too, will see. Never had to replace any, maybe I'm due.

That was one of my first thoughts too. But, after looking at the intake gasket set picture, it doesn't look like water (antifreeze) circulates through the intake manifold of a VX. Because it's running extremely hot, I would suspect antifreeze involvement because it creates lots of extra friction (when it gets into the cylinders) plus it burns hotter. (See if you see any white smoke when it acts up.)

As such, I might be more inclined to suspect a head gasket problem. Certainly water has to flow up to the heads. When a head gasket blows water can get into the cylinders and oil can get into the radiator (fluid). Maybe that's where your oil went?

You need to stop driving it until it get figured out. With the 3.5L engine history, this could lead to BAD news -- if you push it! (I could already be bad news.)

[Heraclid]

Thanks a bunch 89Vette - it is running fine right now, just for a couple of short trips. Plan is to get it to a good mechanic tomorrow for a thorough inspection. I thought I did see white smoke once, but I'm not even really sure and I didn't notice it the next time. But a lot of oil and water seems to have gone somewhere real quick, so that makes a lot of sense. I will mention your thoughts on this to the mechanic. Haven't even spent much time on it myself, things have been kinda crazy and now my brother's wife is in labor and I'm about to be an uncle.

[Heraclid]

Diagnosis was a faulty throttle position sensor, had it replaced. We'll see if that's really all there was to it. Still idling a little bit high.