stalling, rough idling, P0420

Just an update on my earlier post. Still having the same issue, just waiting for lexia to arrive.

The problem now occurs whilst driving, not just when the car is cold. When started in the morning often my C3 will not keep running unless it is revved, it takes about about five minutes of idling before I can get it up the driveway. Other days I have no issue whatsoever, the car runs perfectly.

The problem also continues to appear intermittently whilst driving: extremely rough idling, stalling unless revved, not responding to the accelerator, then suddenly lurching forward. I have no ecu errors apart from a P0420 Error Code: Catalyst System Efficiency Below Threshold.

I am hoping to get lexia early next week, but I just wondered if anyone could shed some more light onto what the cause might be? C3driver52 mentioned the Intake Air Temperature and Manifold Pressure Sensor. I disconnected the MPS and the car still had the issue. Which I guess leaves the IAT sensor in the throttle body.

I know it is hard to diagnose without specific info, but would appreciate any info, as the car is almost undrivable.

Hi here rcombe, this topic https://citroenc3owners.com/petrol-citro ... -t569.html could be similar to yours, water leaking from the washer jet onto the injector damaging it which causes poor running.
This topic https://citroenc3owners.com/questions-about-a-petrol-powered-citroen-c3-f10/le ... -t584.html may help.

There are Injectors for a 1.4 C3 on eBay from £11, not sure if it fits your model, but worth investigating.

Thank you for the link. I did see this when I looked through the forum before. I'm pretty certain I don't have a leak, but thanks for the suggestion. I've had an injector problem before (ended up on the back of a tow truck), but when that happened I had a fault code associated with the injector. Currently its only that P0420 code that I get.

P0420 will need an oscilloscope to look at the waveforms from the O2 sensors, or just change the sensors before looking at the cost of a catalyst

You never know P0420 could be affecting the car, Lexia should help, but doing a visual inspection on the plugs and wiring on the O2 sensors wouldn't do any harm.

This link has a nice description of P0420 https://www.obd-codes.com/p0420

Thank you for the link. I'll have a look at the wiring and see how I go with Lexia.