FOR ENGLISH READER
I searched what to do when I disappeared all cars in the Liberty City, but I didn't get good information or solution. I tried not only Japanese but English searching, but I only reached question thread.
Today, finally I found a way to solve that problem.
To add, this note is for GTA4, I don't know about GTA V.
1.
CLOSE YOUR SPARK IV
That's all. If you don't solve the problem, you'd better to ask someone who professional.