Last week my 2002 Ford Escape started idling rough when the temperature was in the 30-40°F (-1°C to 4°C) range. It also seemed to have trouble shifting or something at 40-45 mph. I'd describe it as a stutter/shudder, and I could see the tach jumping up and down while idling in park.
I didn't have time to get to it until today, and it's in the mid-50s (about 10°C) now. There's really no sign of the previous problems. I turned the car on and let it idle, and I think I felt it stutter once, but then no other signs. The check engine light was still on and there were two error codes: P0401 and P0304.
After a bit of Googling, I think it may be an EGR problem (P0401) and subsequent misfire (P0304). I've experienced rough idling in tandem with the P0401 code before. I replaced the EGR valve about 6-12 months ago and that seemed to have fixed the problem then. I figure that the misfiring is a combination of EGR problems and the cold weather.
Is there something else that could be wrong with my car that's causing the EGR valve to go bad? Or did I replace the wrong component in the first place last time?