Toyota Repair: Previa fault codes, air flow meter, engine misfire

Question
Hi Ted
My 1991 2.4GL Previa(118,000) has a problem. It starts easy and drives ok while warming up. After say 5 miles i put my foot on the gas slowly and the engine doesn't respond until i boot the gas pedal and then it surges forward.  I sent it in to be diagnosed and fault codes 25-26 came up. The guy said it was the front oxygen sensor which i have had bought and fitted but the vehicle is off the road at the moment so i haven't tested it. If the problem persists what might it be? Air flow meter?

Many thanks

Mart
Bristol, UK.

Answer
The 25/26 trouble codes are lean/rich conditions, there may an engine misfire or another condition that is causing this, I really don't think that the O2 sensor is the problem, it sounds it is reacting to the problem with the engine, I would advise you to investigate what the problem may be, it could be caused by a misfire, an intake air leak,even a leaking headgasket, good luck with this.