Jarakana,
Please don't be so hard on yourself, one data point does not constitute a "downward spiral" you need at least 3 in a row. Holy cow, ease up on yourself!!
Paying off an installment does have a negative impact to your FICO score and, it's most likely that the new car loan isn't reporting yet but if I were you I wouldn't expect for the new account to make up for the points lost because your utilization of the new acct wil be close to 100%. Your old acct was decreasing in utilization each month thus adding points to FICO for payment history.
Let me clear up something before I post this, because I know others will want to "help" me understand the error of my ways. I referred to "utilization" for an installment account when in fact there is a better descriptor. On this board "utilization" is used in the context of revolving credit but in my experience, auto loans impact "debt to income ratios", thus loss of FICO points for a new loan as it's a monthly event and you are committed for the entire amount, almost. For me it's just easier to refer to it as utilization and I will apoligize in advance to those who object to my doing so.
FICO scores on November 17, 2014 (prior to applying for and being approved my mortgage)
EX=738
EQ=735
TU=754
FICO scores on March 4, 2015 after being approved for mortgage and buying the home, the mortgage isn't yet reporting.
EX- 689 EQ- 739 TU- 739