There is a sensor/component on the intake manifold called a "choke stove" under the Auxiliary Air Regulator, that is warmed by coolant. I think it's the only part of the manifold that would have coolant. But I don't know how you would get fuel in the coolant tank, though. If you had a head gasket problem, you would see a piston that has been steam cleaned. Maybe it's just a very small head gasket leak, which is why you can't see anything definitive when using the boroscope/endoscope.
Aux Air Regulator;
I found this 20 part YouTube series on the Z/ZX fuel injection along with details about the components, and common issues and things to look for. It was originally filmed in VHS probably in the early 90s.
Edit: the more I think about it, the rough running sounds like the intake/exhaust gasket. But that still doesn't explain the gas smell in the coolant. They have to be separate issues.
Aux Air Regulator;
I found this 20 part YouTube series on the Z/ZX fuel injection along with details about the components, and common issues and things to look for. It was originally filmed in VHS probably in the early 90s.
Edit: the more I think about it, the rough running sounds like the intake/exhaust gasket. But that still doesn't explain the gas smell in the coolant. They have to be separate issues.