I have a 2012 gt 6 speed with an issue of running smoothly at a slight throttle opening. For example, driving on the highway at 70 mph and entering a town with a 50 mph speed limit. As soon as you get to 50 mph, no matter what gear you are the engine will surge, it feels like you are applying throttle and then rapidly easing off. It is almost a bucking sensation, on a small scale, like you are lugging the engine. It does the same thing if you are driving on the highway at 50 or 60 mph and crest a hill. when you ease up on the throttle to maintain a constant speed, it starts to surge back and forth until you apply throttle.

The issue seems to be slight throttle openings between 2000 and 3500 rpm no matter the speed or gear. I have had many high performance, standard transmission vehicles, so I feel that I know how to drive the car. It does not matter if the car is hot or cold, air-conditioner on or off, traction control etc. The car starts great idles about 800 rpm, pulls hard, runs great when you are applying power.

I have had it to 3 different Ford dealers. They have "tuned it" and based off a ford mechanic recommendation, I got the ford racing pro-cal tune and k&n filter, I have always used 91 octane ethanol free gasoline. nothing else has been done except magnaflo mufflers. I am having a new compact MGW shifter installed next week. Does anyone have any ideas how to fix this!

 

Got your PM, here's my list, dunno if I even have it right...

Spark plugs are bad. Or a coil on pack is back. How many miles? Reason I say this is my car was acting like this near the end of the spark plugs' lives. Felt like the clutch was slipping, and it was the plugs all along. Same sorta deal, really, but more on take off than on cruise or hills... but even then, yep, little weirdness going on.

Bad pedal sensor. The blipping would get it out of a dead/confusing spot.

Bad throttle body, in either the motor, sticky butterfly, throttle position sensor... or being dirty, but surely one of those three cleaned it. I am liking the (slightly) sticky butterfly myself, it would do this easily. Unstick, whoops too much... restick... unstick... whoops too much... repeat until blip.

Leaky air tube. Either end or a crack in it somewhere.

Bad gasket for intake manifold, either on the throttle body or on a head port.

Bad MAF or air temp sensor.

Slipping clutch (although I really don't think so in this case.)

Injector issues.

The top three items are my main culprits. Which of these I can't really say. Some of these would throw codes, one would think, but... nothings perfect nor bad enough for some computers, so...

I would get it back to stock tune, paper filter, and then work my way around the problem that way. Mufflers won't matter, don't do that part.

I don't know what else to tell ya. I really think it's the pedal or sticking butterfly, but there's only one way to test that, and that's buy new ones/get them from a junk yard and swap them out. Or individually test them per the manual.

Being a 2012, you should be under factory warranty until 2017 unless you busted the mileage part, so keep on taking it back.. maybe bring a buncha pizza and offer it up to the techs so that you can just chat it out with them... Maybe one of them will go "oh yeah! I know this... bring it to me, I'll fix ya up.'

Ya never know... pizza is magic, right?

I hope I helped, keep us updated!

 

My gt500 does the exact same thing. With the 5.8 in 1st gear the bucking it quite an experience. On the gt500 it's a common problem when you swap out to a mono blade ford racing TB and the tune isn't just right. I read this could be an issue before I swapped it but the tuner told me not to worry about it, he was wrong. From what I understand it's 100% tune related, I always planned to have a custom tune done so I haven't worried too much about it.

Have you changed the TB? Can you convert back to stock tune for a test drive?