Rough Downshift (bog?) from 3rd to 2nd...
 

6AT, driven mostly in manual mode, issue happens in both modes.

Only mods: Unichip EMS, K&N drop-in, Invidia Q300 catback.

I get a pretty rough downshift into second from third, but only when decelerating (to a stoplight, etc). It feels like an extra hard engine brake. If I give it a little throttle and manually downshift, everything seems buttery smooth. So far, I've cleaned the airbox and used some MAF cleaner on the sensor and not much changed related to this problem.

I have a CEL, but haven't gotten it read just yet. Planning on doing that on my way home tonight. Any ideas? I'll post codes as soon as I get them.

Try taking the unichip out of the equation and see if the issue persists.

Yeah, if your "only mods" list includes a reflash, I would consider eliminating that variable before assuming it's something in the transmission. Read the code, return to stock tune, and see if the problem goes away (or if the light comes back).

The Unichip isn't so much a reflash as it is a piggyback, which I can see causing issues more easily than a reflash like ecutek. Piggybacks essentially sit between the ECU and the sensors on the motor and modifies the signals before passing them on in an attempt to trick the motor into performing in a certain manner. Definitely not the cleanest way to go about things, could easily confuse the ECU.

My only concern with that is that I've been running the Unichip for months, and the problem is only days old... Nothing changed in that equation which makes me curious. I'll definitely try removing it after I read the codes though!

Hm, that is weird then...good luck!

I've been happy overall with the Unichip, but the only reason I'm doing it over a tune is because there aren't many Ecutek tuners (or even dynos) within a reasonable distance from me. Piggybacks are certainly not my first choice :(

Update: scheduled a service appointment.

CEL was unable to be read -- link/communication error with and without the Unichip. While trying with the engine on (first attempts were accessory mode) I noticed a rough idle and could see the shift knob visibly vibrating. I normally don't leave it idling that long, so I may just have never noticed.

I've seen the TSB for cam position sensors/rough idle and am suspicious that I am also a victim of that one!

I'll make sure to check back in after the service reps look at it tomorrow morning.

So, the dealership claims that the engine is running rich, and is attempting to blame that on the K&N filter (of course). But that seems counterintuitive -- the car should be running leaner on a higher flow filter if anything... Especially since I went ahead and pulled the MAF sensor and everything looked super clean. I'm guessing that the Unichip was adding a little too much fuel for my altitude, which is pretty high.

Funny thing is, though, that after removing the Unichip yesterday, my bog was completely identical. Maybe the ECM learned bad behavior? Or more likely, the CEL was unrelated to the light bog-like feeling I'm getting from 3rd to 2nd. They're resetting the unit today and I'll see if the ECU reset+lack of Unichip makes any difference whatsoever.

I may consider leaving the Unichip off, or grabbing Torque and making sure my A/F ratios look good and everything -- maybe even running a fuel out map on the Unichip if it reads rich.

I'm just still not convinced that this downshift bog is related to the Unichip or my airbox/air filter. We'll see in the next day or two as the ECU relearns... After an ECU reset everything seems initially okay.

EDIT: Dealership reported the following codes:
P0172 (Bank 1 Rich)
P117B (Fuel System Abnormal (Di))
P1170 (Fuel System Abnormal (Port))