My wife's 2013 3.5l Explorer is surging at part throttle. It's smooth as silk at 70mph, steady at 2000 RPM, but accelerating gently or holding steady at 45mph or so makes it surge (the tach confirms that it's not just my imagination).

It acts like a bad TPS so l loaded up the parts cannon and replaced the entire throttle body... the problem is still there.

What else could it be? No codes to read.

Ancillary question; This is the first push-button start vehicle that I've worked on, so how do you get your code reader to pull codes without starting the vehicle (as opposed to turning the key to "RUN" on older vehicles)?

 

If you push the start button without pressing the brake, this should put the vehicle into the run mode or accessory on mode without starting the engine.

 

THe reason it runs good at speed is because the leak is minor compared to amount of the throttle air coming in . I find that a homemade smoke machine off you tube is best to find the leak .Check your purge valve for leak thru too .