Mk4, here you have it!!
I hadn't shown it yet. Well, here's the little 1J1. There's still work to be done under the hood, but after replacing the injectors, spark plugs, air filter, oil and filter, power steering fluid (it had the generic red one, not the green), cleaning the intake (throttle body), and adjusting it mechanically, the car has made a huge difference!
Now it doesn't have an unstable idle, it doesn't rattle, it doesn't smell of gasoline, and it doesn't seem to be leaking fuel into the crankcase (it used to). It's smoother, runs much more efficiently, and is faster, as much as is possible with a 1.4 16v...
The next step is to check all the sensors with a multimeter. If any are damaged (which doesn't seem likely), replace them, and check the vacuum line. Then connect an OBD2 scanner, and finish tuning the engine. Then I'll replace the silent blocks and remove the air conditioning compressor.
From here I'll start with the aesthetics, weight reduction, bodywork and paint, and some interior work... There's still a way to go, but mechanically I can see the light at the end of the tunnel, and that gives me strength.