i have a 94 honda civic 1.6L and my speedometer is 10mph off while im driving it but if i drive it for a while it goes to 0mph please help

 

When the speedometer drops to zero, check if the odometers also stop, or if they keep rolling up miles. If the odometer keeps going the problem must be the speedometer head. If the odometer stops it could be the speed sensor. In that case the first thing would be to check that the sensor plug is secure and not corroded (the sensor is on top of the back of the transmission, above where the axles come in). A problem with the sensor will also usually turn the CEL on.