I'll check the ground on the ECU (as well as the other firewall mounted stuff) to make sure.

This is a new car (for me). I just got it in November '18. Nothing at all has changed since I got it, other than the recent parts swapping I did (fuel pump, coil). The drive train and engine compartment were rebuilt & refurbished by a prior owner and there's only about 2K miles on it since.

Thanks.