Car Mechanics (UK)
I hope you can shed some light on a problem with my three-door 2001 Toyota RAV4 NRG VVTI. I’ve owned the vehicle for two years and have been impressed with how it drives. After the 2018 MOT, where it initially failed on emissions, my garage changed a Lambda sensor and the car passed.
Since then, I have only used Shell V-power or BP Ultimate fuel and, on the last fill before the 2019 MOT, I put a bottle of Forte fuel emission system cleaner into the tank. The car subsequently received a fail certificate, which detailed the following: Exhaust hydrocarbon content after 2nd fast idle exceeds default limits (184.108.40.206(b)) Exhaust Lambda reading after 2nd fast idle outside specified limits (220.127.116.11 (c)) Exhaust carbon monoxide content at idle exceeds default limits (18.104.22.168 (b)) The tester’s comment was that it is running too rich. My mechanic changed the second downstream oxygen sensor (bank 2 sensor was changed at the last MOT). The engine did not reach the levels required at another check.
Then the catalytic converter was changed and it passed the emissions test, but at the upper end of the limits. The engine coolant sensor was also changed and, although the limits remain within the parameters for a pass, my mechanics are concerned that the high level means the cat may be destroyed by next year’s MOT. The garage’s diagnostic equipment picked up that the sensors were now all signalling, but obviously it is not a Toyota main dealer, although my mechanics felt that the level of diagnostics required should be adequate using their equipment given the age of the car. Having said that, the high-level has not yet been addressed so your thoughts would be appreciated. Other information from the V5: Variant ACA20(Z), Version ACA20R – AZMNKW(2B) 1998cc CO2 211g/km VIN and engine number supplied. Exhaust Emissions CO (g/km or g/kwh) 0.610 – HC (g/km or g/kwh) 0.070 – NOX (g/km or g/kwh) 0.040.
I would agree with the simple explanation given that your Toyota is running rich. The problems addressed have so far all been attacked from an engine management perspective. Changing the 02 sensor and the temperature sensor are all actions that would encourage the ECU to lower the fuel content. Replacing the catalytic converter would initially compensate for the richer mixture, as it has done, but over time this will again fail, as you fear.
I would consider the possibility that the injectors are worn and allowing too much fuel into the manifold. This would account for the rich mixture and, at some point, no amount of electronic control will reduce this. The injectors are easily removed, so it may be advisable to have them checked.
One other component which has not been mentioned is the MAF sensor, which on your Toyota also incorporates the air temperature sensor. Although the MAF sensor is difficult to check using a scanner, the air temperature should be checked to ensure that it is giving accurate information to the ECU.