My 2009 Honda Fit is slightly bucking and sputtering when accelerating AND also at stop. No codes. Background: Just had 2 tranny speed sensors replaced as that was original code that came up with bucking problem and flashing "D" gear light. Problem persisted so took to dealership. Installed OEM Honda specs oil filter installed, new fuel filter, fuel injection cleaned, did tranny flush and fill. Tune up at dealership last year with Honda OEM plugs). The dealership ran it for 30 miles hooked up to a computer diagnostics and everything checks out. No codes pop and still has light kicking spitting persists. Thoughts? Bad fuel pump...clogged fuel lines?

 

So to clarify, no more light, right?
are your RPMs steady when accelerating, or to they move in an odd fashion? Somethin like that would indicate to me a fault with the throttle position sensor.
Now, if youd be so kind as to check/send images of all four of your spark plugs, that would say a whole lot. It'd rule out or verify any concerns with the fuel system/intake. I wouldn't be surprised to hear another loose spark plug story since its so damned common. I think instead of vins I'll just print out forum threads for honda, hah!
Sensors do fail, sometimes due to faulty manufacturing, but an HDS would pick up on something like that.
To test out your fuel pump is usually pretty easy. There's gonna be a little shrader valve somewhere in the line that'll let you spray the stuff everywhere. Plus! You can put your key in the ignition and turn it to on, where all the indicator lights turn on, and immediately listen for a wooshing sound that should last a bit over a second.

 

Tough to know from the desk here in China.

Look for vacuum leaks with smoke test etc.

Dirty throttle body will prevent proper idle and drivability issues. Easy to clean (there is a special fluid for that and some instructions here regarding moly grease)

Clean your MAF also (use special fluid for that).

Check air filter is clean.

When is the last time you changed the battery? These tiny batteries don't have a lot of juice. Low power will cause some systems to become flakey, although other systems can run fine on low voltage. Get battery load tested at battery store or DIY load test.

Do a voltage drop test to make sure your main wiring at battery, alternator, to electronics, and all major grounds are good.

I have had bad throttle position sensor cause occasional engine racing/sputtering on a GM car. Very difficult to diagnose. Easy and cheap to replace. I don't know if that is a common Fit issue.

 

Plugs is the go to now looks like hehe.

 

Yup...so checked/repaired all the issues from people's responses. Very helpful so thank you all. It ended up being a bad transmission. Pile of metal in the fluid. Put in bottle of Lucas Transmission goop stuff for now. Ordered used tranny off Fit with only 47k miles. Will be installed by Tuesday by a shop. All in"?: $1300 parts labor/tax. The Fit shall live on!!

 

Really sorry to hear that, and surprised too. thanks for letting us know.