Can an untrue wheel cause up down jerks?
Yes.  It's possible.  Newly laced wheels often have "flat spots" where the rim is out of round.  Generally you round and dish the wheel before you start trueing it.  It's possible that the wheel has a flat spot that you are feeling.  

However, there are another possibilities to include bad tyre mounting, improperly secured wheel (axle), bad tyre and assorted drive train issues.  It may be best to have a mechanic or experienced home maintainer check it out.