Fuel Injector code P0172 'Too Rich'

Our VIN #148 (2000) has had four O2 sensors replaced under warranty.
In 2004 we footed the bill for yet another O2 sensor out of warranty.

Now this month we have a similar idle surging issue (200 - 2500 RPM with stalling, battery drained, engine light on), and took it to the shop. Shop says code # is P0172, which means 'fuel mixture too rich'. They want to replace the fuel injectors (three of them I presume) for $850.

We purchased this car to a) save the environment and b) save money. If we have $1,000 repair bills every year we cannot meet objective #2.

Service man says the fuel injectors need to be replaced -- so I ask this forum:

Why so many bad O2 sensors, and why now the fuel injectors?

Cannot the fuel injectors be flushed or somehow cleaned, rather than replaced?

Thanks.

Geoffrey Smith
#148
Red
Stick
Cal Lic 'CLEANER'
858.442.1425