My 92 TR 4cyl (185kkm) has developed a strange problem - it runs fine for the first half hour or so after a cold start, then it loses power and surges when i give it a bit of throttle.
Turning it off and waiting for a few minutes solves the problem - for the next half hour. This will happen sooner the more power I use i.e. when driving up hill.
Also, idle is pretty low and rough especially with the aircon on.

I've used a bottle of injector cleaner, and blown carby cleaner down the throttle body. No effect whatsoever.

Question is, what would you try first? TPS? ISC? Clean the injectors? Something else?

Check everything from the MAF back for air leaks. Check MAF plug and socket for corrosion. Possibly a combination of air leaks and a bad ISC. Collapsed cat or muffler could be another possibility.

I just changed the ISC and TPS. The idle is better now, I think the ISC was stuffed.

Where is the MAF? Is it that black box on top of the air filter?

Yes, big black box with the air cleaner in it.

What does TPS stands for?

Throttle Position Sensor.