I have had my car for about 4000 miles now. When I am curising at lets say 50, the rpm will go from 1500, drop to about 1000 for maybe 6 secs, and than shoot back up to 2000, its not as long if i give it any gas. It seems to be bogging really bad. I do not know if the fuel filter is bad or not, but the last guy who had the car definetly looked liked a cocaine dealer, so maintenace wise i dont think the fuel filter nor transmission fluid has ever been placed. So its my throttle response and bogging a proble because of the fuel filter or is it something else?

 

Change the fuel filter anyway but it is not your problem.

Is your car an auto?

 

ya, its an auto

 

When you buy a used car, maintenence is always a question. Unless you know for a fact that the maintenence has been done, you must assume it has not been done. That means that you have to do it. You should replace all fluids:

coolant
oil
rear end
tranny

You should inspect and replace if necessary:

belts
hoses
spark plugs
air filter

Replace the fuel filter.

 

As soon as I got my car, I parked it. I put it in the garage on jackstands. It sat there for over a month while I did the following:

Fuel Filter
Silicon hose job
Mazda fuel line recall kit
Fuel pulsation damper
Fuel injector overhaul
Check valve testing/replacement
Solenoid testing/replacement
Rewrapping of the main engine harness
Fuel pressure gauge installation
Fuel pressure regulator testing
Spark plugs
Spark plug wires
New oil + filter
New coolant
New transmission oil
New differential oil
New airbox filter/airbox mod
New oxygen sensor
Installation of an aluminum AST (air separator tank)
Brake booster line/check valve

It was a lot of work, but my car has been good to me since then.

Most (if not all) of the above should be mandatory work on a used car with an unknown maintenance history. (IMO)

Sonny