engine problem

Hi,

Here is problem:
1- sometime i hear knock sound if drive car from 0 mph with second gear

2- if i press brake pedal, rpm's idle drop down to 400.

3- sometime my engine shake quick just one second (look like you turn the key off and you turn on quick)

but this three problems does not always happen only once a day.

4- my car become very slow and no torque hard to reach 80 mph.

i do everything change (air filter, spark plugs, fuel filter) clean throttle body and clean fuel injection

but nothing changes still same problems.

thanks