I recently purchased a 90 GX and it's got some problems. It is a hard starter and generally poor runner. The Ecu is throwing codes for the tps, the air temperature sensor and the afm. Is it more likely that all of these components are bad or is there a common ground or ecu problem here?

 

Check the ECU Ground first off/re-ground it.

TPS is a common problem (if it's done broke your idle will 'hunt').

 

Where is the ECU hiding on these cars? Is it in the passenger footwell?

If the AFM is bad, would it cause poor running and very rich conditions?

 

Passenger footwell, rip up the carpet, you'll see a huge metal plate; it's behind that.

As for the AFM, I have no idea.