2002 Ford Expedition P0401 and P0402 EGR Valve Codes Causing Rough Idling?
My 2002 Ford Expedition has recently developed two trouble codes: P0401 and P0402. I replaced the EGR valve over six months ago, and at the time, my local oil change facility advised me to ignore the check engine light. However, this week my SUV began running very roughly—almost as if it's misfiring. I recently replaced the fuel filter (at 58,000 miles), but that did not resolve the issue. Now I'm wondering whether I should replace the spark plugs to fix the rough idle, or if I should instead focus on resolving the persistent EGR-related codes. Could P0401 and P0402 be directly causing the misfire-like symptoms? I need guidance before spending more money on a gas-guzzling vehicle. Thanks for any advice—John
John, it's important to stop replacing parts without understanding the root cause. OBD-II codes like P0401 and P0402 are designed to point you toward specific issues—don't ignore them. I recommend reviewing these authoritative resources for detailed explanations: https://www.obd-codes.com/p0401 https://www.obd-codes.com/p0-402