Hi , My 95' volvo 850 turbo used to be hesitation while accelerate from idle , and sometimes I stop from running the idle rpm run below 700~300 , then back to 700 about seconds.

I had replaced the Mass air flow sensor , it become much better , but the problem still happen sometime . Especially weather is hot ( > 30 oC , in Taiwan )

I had use a digital voltage meter to measure the signal ( black wire on my front oxygen sensor ) , while it heat , the voltage keeps high ( about 0.6 ~ 1.4 ) .

The error code from ecu is 2-3-1 . It happend error code , and always gone after 1~2 day(s) .

The fuel comsuption is keep reasonable , about 11.5~12 liter / 100km .

Should I replace the oxygen sensor ? I am planning to replace it with a bosch universal oxygen sensor .