AD595AQ for Car Exhaust Gas Temperature

No I haven't, but does that solve my grounding problem?

No, only in the sense that it might correct the problem that we haven't been able to sleuth out yet. Plus I just like the fact that it has a digital interface so it leaves out some steps in processing the data.

Without looking at your project, I'm at a standstill. Can you post the EXACT schematic diagram and some closeup photos of all sides of your physical circuit?