I had this problem with the S2 Roadster and still have it with the Aero Plus 8.
Always the N/S downstream lambda sensor slow to respond.
After talking to may people and trying different fuels I started keeping a diary, noting when it happened the weather, driving conditions and style. I've done this for over 30,000 miles.
Conclusions: it happens when the cat gets cold and isn't working optimally. This seems to be caused by the weather and by how you drive: if I keep the revs above 30% and vary the throttle opening frequently it doesn't happen, so enjoying the car on a B road it is fine.
If I have been pootling along in top at 50mph in traffic on an A road, then suddenly change down and accelerate hard to overtake it will most probably happen and if it is below 10C then it will certainly happen
Choice of fuel doesn't seem to make much, if any, difference.
Short of insulating the cats and exhausts and fitting spacers to the cats I don't see a solution.
It is easier to clear the light when it happens.
Bottom line: "they all do that sir"
More seriously, it isn't a fault, it is an observation and it is caused by putting a large and powerful engine in a small light car, so it isn't working very hard. So drive it like you stole it and all will be well...
I don't want to be pedantic, but I suspect these are different problems. The
downstream sensors, as in Peter's case, have purely a control function. They simply monitor whether the catalytic converter is working properly. Mostly it is connected to the DTC 420.
https://www.obd-codes.com/p0420With OBD2, you can see in real time if the lambda sensor downstream is bouncing or level. If it is bouncing, the catalytic converter is not working properly. But that means the probe is ok, just showing bad news.
It seems plausible that the catalytic converter does not reach its working temperature to cause this fault. A sporty driving style is a countermeasure as in Peter´s case. Or the catalytic converter is faulty. All this has no influence on the engine performance as long as the cat is not blocking the airstream (I had this case with my Elise when the internal grids were pushed to the output pipe of the cat).
DTC 133 refers to the engine control and concerns the
upstream sensor(s).
https://www.obd-codes.com/p0133On my 4/4 this upstream sensor was faulty after 80,000km and the DTS was reported in OBD2 (but not in the MIL!, Ford is very "tolerant" there). A new sensor resulted in better performance and significantly less fuel consumption. It is also possible that the MAF sensor is not working properly or that there is a leak in the upstream gas pipeline (intake and/or outtake) that is giving the wrong values to the sensor. Then it tries to readjust, and it can happen that the engine always runs too rich, which unfortunately contributes to the probe getting dirty, a vicious circle. This could also be the reason why your sensor, meabh, is defective again after so few miles.
I would also look at the MAF sensor and check all connections from the air intake to the lambda sensor for leaks. Because, to me, it sounds like an undetected fault, and therefore and a new S1 sensor again could probably be both...the causal fix or unfortunately just a temporary symptom improvement.
If you can, try very carefully cleaning the MAF sensor with a special spray that won't break anything. This would be the cheapest and easiest point of a start. Also clean the electrical plug with a appropriate spray (let it dry before reconnecting). You can e.g. read your OBD2 when just switching on the ignition with cold! engine if the MAF sensor shows a plausible environment temperature or not, but this is only one of the MAF´s jobs).
