My car does not rev past 4000 RPM

My car does not rev or when driving does not go past the 4000 rpm. I have tried putting the code reader on the car, but it is not reading any codes and there are no lights on the dash. I thought it was the MAF, but looking for hours found that this Honda Civic 1.6 vtec 2004 does not have one. I have look on the Internet, but all people say is to check the oil and make sure it is full and it is.