2011 Mustang GT bucks after cold startup

I bought the car new in 2010 and from day 1 it has done this after a cold startup. If I drive with a steady light throttle it will buck two or three times before running normally. In addition, if I start the car while it's cold and let it run until it idles down the RPM will kick back up two or three times before settling down to a steady idle. I've tried the idle relearn called for in the owners manual several times and the car will idle and drive like it's supposed to for a few days before the condition starts to return. Three years ago I took it to the dealer twice for this and both times they said they didn't find anything wrong. Since then I've just been waiting for HPTuners to release support so I can try to figure it out for myself. Now that it's here I'd like to give it a shot. I'm just not sure where to look. Any suggestions? Is there anything I should look for with the 2.24 scanner?

First thing I would recommend is that you have the car reflashed with the latest OS for your car, as there have been several revisions. I have a 2014 myself, and the stock tune does have quite a few quirks.

I hadn't thought about having that done. Is it possible to write a 2012 with HPT once they start showing up in the repository? Or even a 2014?

Yes, you could do it.

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Originally Posted by Blazin72

I hadn't thought about having that done. Is it possible to write a 2012 with HPT once they start showing up in the repository? Or even a 2014?

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I wouldn't write over your 2010 with a 2012 file. I'd just have Ford install the most recent flash that shows up in their database for your VIN number. It sounds like a strange drivability problem that the calibration engineers probably figured out and fixed...just not until after your car was sold. After that, then if you wanted to use HPTuners to find more power and whatnot...you could tune from there, and keep that file as your "Stock" file from Ford.

I'm going to bring this thread back because there is a discussion on another forum about this right now. I'd really like to try and learn what causes and how to correct this. But I'm not really sure where to start looking other than I'm guessing it has to do with one of the tables relating to startup. It's most pronounced on cold startup, usually 30 seconds to a minute after starting.

I updated to the latest TSB (11-7-4) for the car and it still does it.

I'm not sure if Ford has fixed it. My 2014 (latest calibration) would actually try to stall if I touched the throttle right after a start up (cold or hot) and it was totally stock.

Mine does this as well. Even tuned. I usually don't drive it cold so it's a non-issue for me.

Would be nice to know what causes it, though. I haven't put too much effort into it so far. Maybe I'll look at it soon.

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Originally Posted by Gremlin85

Mine does this as well. Even tuned. I usually don't drive it cold so it's a non-issue for me.

Would be nice to know what causes it, though. I haven't put too much effort into it so far. Maybe I'll look at it soon.

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Yep, I need to sit down and iron it out. Just gotta find the time.

One of the things that I have noticed is that the car will slowly start to accelerate before abruptly slowing down, which is where the bucking comes in. This all happens without moving the accelerator pedal. I am guessing that it happens as the car transitions from open loop to closed loop after startup. I've included a .cfg that I put together. Is there anything else that I should include? I'm not very familiar with using the scanner.

I'm learning from the ground up and would like to focus of basic drivability before much of anything else.

I'm going to bring this thread back again since I think I've got the problem under wraps.

The first thing I did was zero out the Fuel Base Cold Enrich Decay table from 20* to 90* and 5 seconds to 20 seconds. This made for a very noticeable improvement after cold startup but I still had some issues if I had driven the car then let it sit for an hour or so before driving it again so I ended up zeroing out the entire table.

After doing this there was still a "transition" that could be felt so I raised the CL 02 Sensor Temp value from 150* to 275*. I did this after noticing that the 05-10 files all had 500* set for their enable temp. I've been driving for about a week now and haven't had any problems.

If anybody else is having a similar issue I'd like to see what you think of the changes or if you have any other ideas.