Replaced the battery connector hacks with a pair of proper connectors that attach a Euro-style battery (terminals on top) to US-style wires. Cleaned up all the terminals & connectors.
Replaced the ground cable from the battery to the engine block.
Opened and re-tightened the TBI mounting bolts to correct torque (22 Nm).
The coolant fan switch cable is disconnected (and covered with tape), since I don't have the new connector yet. I tried grounding the wire (with the engine off, battery connected). As I understand this should have started the fan, but it didn't.
Nothing has changed. The car starts well when it's cold, but after 10-15 minutes, it starts to choke violently and the engine dies off. All coolant and engine temperature look normal in WinALDL.