Avensis Rich Fuel Mixture

[brushman]

Does anyone know how to correct it? The car is a 2001 avensis estate 2.0 vvti. It has a fault code showing lean fuel mixture and I think the resulting ECU adjusted rich fuel mixture has messed up the Cat so it won't pass its MOT. No sensor fault codes are showing as it's a replacement engine, on the previous engine O2 sensor fault was showing as well as the lean fuel mixture code. Car will hardly accelerate at all in higher gears or uphill and judders/ misses at idle.

What would updating firmware/software of the ECU do? Would it correct the fuel mixture? Thank you.

[Black Knight]

Mucking about with the ECU probably wouldn't help. It's getting a signal from somewhere telling it it's running lean and hence responding by changing the Air/Fuel ratio.

First guess would be air flow sensor going on the intake system. As they age they tend to lean the mixture out.