2018 ford transit van 350 hd when going 70mph it will randomly slow you down to about 35 untill you pull over, shut it down and wait a few minutes. There is no check engine light or codes and the dealer cant find the problem. Thanks all
Another thing to check would be excess back pressure due to a clogged catalytic converter.
https://www.youtube.com/watch?v=qJTmddbOxMk
Possible partially clogged fuel filter.
would that throw any code? and would that be the reason that it is totally unpredictable? thanks doc
Nah diagnostics are pretty dumb when it comes to fuel supply. Kinda weird
I would think it would throw an injector code (lean) but I'm not qualified to answer that question. Your problem seems like a partial fuel starvation problem. I'm sure help from other members will be forth coming. Other things might be a clogged air filter, dirty MAF sensor, throttle positioning sensor, etc.
i did change out the throttle body on a whim, but alas no change