P0402, is it my EGR valve?

Good for you. My older Ford truck’s EGR system develops problems once in a while, but the cause has always been due to carbon deposits clogging the passages that route the exhaust gasses back into the intake manifold rather than the valve itself. My truck doesn’t use a computer that monitors the pintle position. The engineers who designed my truck in those ancient time, if someone had suggested a truck would one day have dozens of computers running the show, measuring this, actuating that, they’d have said you’d been smokin’ loco weed … lol .

Well I have to assume it’s deposits that were the problem for me but I’m not a complete amateur when it comes to cars. I’m honestly stumped what I did clean has made any difference. You could practically see the chrome on the walls so to speak… after I took it off and saw the inside, I only sprayed it out and reset the light out of an effort to 100% diagnose the issue. I really didn’t expect it to make any difference.

I’m still expecting it come back, but I’ve put about 200 miles on it since then, and it still hasn’t come back. I’ve run it in all kinds of conditions too… done everything from drive it like a granny to driving it like I stole it.

Well it did come back eventually. Finally found out what the problem was though. PCM. At one point I had something like 12 different codes. All 4 O2 sensors, EGR and other related emissions systems, ignition circuit issue and also ac clutch short. Did some testing and confirmed the problem wasn’t the wiring or O2 sensors per the Ford diagnostic manual. The end of which calls for replacing the PCM. Which fixed the issues.

Posting this in case someone else comes along with similar issues. In all my googling they’re were tons of threads where people never updated what the problem actually was. I can’t remember where but there’s at least one other thread whose mustang had like all my same issues, no one ever said PCM. That guy is probably still waiting for answers lol.

Thanks for for posting the successful results @Iamsupernova5891. We need all the help we can get to keep us looking intelligent. Wearing bifocals and driving a Volvo doesn’t fool anyone these days.