I would use 122 baud.
Looking at the picture I guess the timing is (4674-4608.4)/8 = 8.2 and is 122 baud.
Suppose the timing is the magic number of 8.192 ms (2^13), the baudrate would be 122 baud.
Suppose we have a clock of 1MHz, and we would use a divider of 8192, the baudrate would be 122 baud.
Wikipedia about OBD1 : On-board diagnostics - Wikipedia
It seems that some use 160 baud, but no standard protocol is used for OBD1.
So you have to find the protocol used by your car.
I can find many examples of OBD1 and Arduino, like this one : OBDuino - Wikipedia
That article has also many links.