2010 GT Experiencing a Flat Spot/Bog

Road_Trip

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New to the forum and just getting back into Mustang's after quite a long spell without one. I've had 4 Fox bodies and an 03 Cobra in the past, so I'm not a total noob when it comes to finding my way around a car.

Just bought a 2010 GT coupe, manual transmission and 3.73's, with 27,600 miles on it 2 weeks ago. Drove it home 700 miles the day I bought it and loved it, but noticed something a little odd. While having the cruise set, if I was anywhere around 2100 rpm or so, and I'd hit a slight incline, the car would struggle to maintain speed and then all of a sudden surge to the set speed. Seemed odd at the time, but the car ran great otherwise. It did this the entire trip home. Fast forward to the day after I got home and I noticed anytime I was in the 2100-2400 rpm range, it really bogged or felt like a flat spot when trying to accelerate, in any gear. Best way to describe it is turbo lag, despite being n/a. I'd hit the gas, anticipate the acceleration and it would take a couple of seconds to really get it going and out of that RPM range. 2500 rpm and up, no issues, regardless of gear. Starting from a dead stop, no issues getting up to that range and then it just kinda slugs through it.

I've got a fuel filter and plugs waiting to go in it this week, but I don't think that's the issues. It seems to pull fine through the power band once I'm above 2300-2400 give or take. I've pulled the mass air meter and cleaned it out. Hooked up the scanner and it has 0 codes and 0 previous codes. To my knowledge, the car does not have a tune. Appears to only have a catback, Air Raid CAI, and slightly lowered on 19's. Car idles great, cruises great on the highway and surface streets, just has the dead/flat spot/bog/sluggishness.

Any ideas what could be causing this? Any help is appreciated!

Thanks!
 

Midlife Crises

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Your 2010 GT had a very good closed cold air intake on it when it left the factory. Try to find a 2010 air box and duct and restore the inlet to stock and you may find the funky lag goes away. Also the low miles are great but the car is old enough for some of the rubber hoses to degrade. Small vacuum leaks can be a real pain.
 

Road_Trip

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I've been debating hitting the local junkyards to see if they have any air boxes; can't say I'm a fan of this CAI they installed. Got a smoke machine on the way and it'll be here in the morning. I've been wanting one for the garage anyway, so figured why not.
 

The Fixer

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My son's '06 has a surge/flat spot in that same RPM range, running with a K&N intake tube and cone filter or the stock airbox. His car has IMRC delete plates though so we assumed it was that combined with the stock tune.

The car came with a programmer so we loaded the aftermarket tune and added the bigmouth JLT intake that also came with the car. It still has some hesitation in that RPM range, but it's much better than before. Still not sure why, and it runs pretty rich.
 

Dino Dino Bambino

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I suggest you:

1. Thoroughly clean the inside of the throttle body if you haven't already.

2. Remove the insert from your CAI and get a tune from either Brenspeed or Lito.
 

JC SSP

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Welcome and post some pics of your new ride.

I recommend the basics. Look for vacuum leaks, new fuel filter, oil & filter, check spark plugs, clean TB, MAF, air filter, etc before you start to invest in anything else.

Run a can of EFI cleaner through the tank w/93 (high test) and maybe a little sea foam through the intake/engine to clean her up before you do the oil change.

Just my .02 cent.
 

Road_Trip

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Thanks for the input from everyone. I'll run the smoke machine either tonight or tomorrow and get back to you guys on that. Trying to get work schedules lined up with my youngest son so we can do the plugs and fuel filter together. I'll pop the intake tube off when we do the plugs and take a look at the TB to see if it's got any crud built up on it. Sadly, we can only get 91 octane here, but I'll throw some fuel injection cleaner through it on next fill-up. I'll get some pictures posted up once I can get to the car wash; weather and roads have been crap since we got home with it.
 

Road_Trip

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Ran the smoke machine on it for about 3-4 mins this evening and didn't see anything coming out except from the filter. Man that stuff stinks! Cleaned the throttle body out and the blades but there was minimal crud in it. Took it for a drive and still have the issue. Trying to do one thing at a time, so we'll get the plugs and fuel filter changed out this weekend. After that, we'll get some fuel cleaner in it and go from there.
 

Road_Trip

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My youngest son and I swapped out the plugs Friday. Have to admit, easiest set of spark plugs I've ever changed out, even compared to my old fox bodies. Took it for a drive Friday afternoon and didn't notice a change with it. Tuner showed up last night and I'll work on getting in touch with Lito to see what we can do for it. Threw a can of Berryman's in it too, but haven't been able to drive it yet. I've got a truck load of goodies coming for it later this week, and it snowed last night and into this morning, so it's not going anywhere anytime soon. I appreciate all the feedback up to this point! I'll keep the thread updated as I move forward.
 

Road_Trip

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It's been a busy week, but I believe the issue has been worked out. I've had a lot of email conversations and 3 tunes from Lito, and the car is running amazingly well. The bog/lag/dead spot appears to be gone and the car has become very responsive in the 2000-2600 rpm range now. I appreciate all the feedback and suggestions while working through this!
 

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