hi,
Fico likes to see an installment loan reporting - credit mix, just like Fico likes two bank card CC's reporting as well, as well as the low utilization 1-9 percent.
when I paid off my ONLY installment loan, TU dropped a handful a points and EQ might have gone up a few points. Some auto lenders use auto enhanced scoring and depending if you were a good boy or girl in the past, you'll either see a higher or lower score on the auto version. For example, I know my TU Fico Score at the time I bought my car was around 685, however I think my lender may have used auto enhanced b/c I did get the Tier 1 financing. I had two positive never late autos reporting...a good thang!
Adding a new tradeline, such as an auto loan could affect your AAoA - it also could not affect it - it depends what your AAoA is at the moment.
I started with an AAoA of about 7 years and didn't dip below five years and I didn't see a ding. However, I believe and I could be wrong, if I dipped below the five year AAoA mark, I would get punished a little bit more severely.
I hope this helps.
Starting Score: 682 EQ, 663 TU