You can adjust the carriage at the back and under of the extruder carriage. It's the 2 screws that hold the 2 white teflon blocks in place. Mine was loose and if i shook the motor it would wobble the entire carriage. Don't tighten them too much or the carriage wont move at all, just tight enough so that there's as little wobble as you can get and loose enough that there is free motion from left to right. There is the Solidoodle extruder head wobble preventer (shown in the picture below) but i never got around to trying it out.
The extruder can be tightened using a wrench or ratchet under the wood plate and using something to stick in top holes to prevent the screws from spinning. I tightened mine but it always came lose after a while because the wood would just bend with the frequent temperature changes. Fixed it using Lawsy's jigsaw replacement.
(These aren't my pics, i was too lazy to take pics of my own.)
I still can't print perfect circles or precise parts, but it did make all my layers more uniform. If that doesn't help and you've done all the calibrations that are recommended, then you probably need to fix it in the firmware.
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