Hi my name is Patrick, I have a 2002 mitsubishi lancer. It recently stalled when coming off the interstate and to get it to run without it stalling again I'd have to stay on the acceleration pedal. I took it too a shop and the guy told me it was my idle air control valve so he replaced that. It worked fine a couple starts but then it started to stall when I first started it so I had to press the acceleration for a couple minutes until it could run by itself. It seems to run fine after 10 minutes of being on but the first 10 minutes it runs rough. I took it to an autozone and it brought up a p0421 code. I replaced my top o2 sensor on it but it still didn't change anything. I'm just wondering if you could help tell me what you think is wrong with it. Do you think it's a clogged catalytic converter?
Always research 1st before replacing parts. Check bulletins and recalls.
https://www.mitsubishi-forums.com/attachments/recall_pcm_reprogram-pdf.3605/
https://testing-public.carmd.com/Tsb/Download/23283/520045021
It could well be a clogged cat (on Lancers it is pretty common), but just replacing a cat without checking is too expensive. You will need to go to a mechanic who can measure the cat counterpressure (= pressure drop) and then decide. I think Scotty had some video on how such measurements are done, but I cannot give you the link right now.
AND: it is not necessarily a _clogged_ cat: it could be that it is just an old worn-out cat which does not do its catalytic job well any more. A good mechanic can tell this as well, by comparing both O2 sensors´ readings under various conditions.
