Pulse Counter RCM2000

Ive been doing a program that can detect the pulse with a frequency of 1Hz to 200KHz. I use the interrupt and costate with a 1 second delay for reading the counted pulse. The program works well with frequencies between 80Hz up to 8.5KHz. But whenever I set my frequency to less than 80Hz I get a reading which is bigger than expected. Whenever I set my frequency greater than 8.5KHz the program time’s out. My processor chip is IQ5T.

Can any one help me?

Thanks in advance.