Hi,

My speedometer was perfectly fine until one day the fuse blew.. after i replaced the fuse .. the speedometer is working but its not accurate.. its lik around 5 km off..so for example. when im going 120 KM/HR its really going like 115km/hr.. also when the engine is cold and i start the car each morning to go to work... the RPM would be a bit above 1. then as the engine gets warmer.. the rpm slowly goes down to 0.5

 

The RPM is correct. That is how it is supposed to perform.

How can you tell the speedometer is off?
How could you tell it was accurate before the fuse blew?

According to my Garmin GPS - almost every car I have ever put it in reads about 3 mph faster than the actual speed......

 

you know those new honda civics with the digital speedometer. i was beside it going in the same speed as that car also.. the civic is going on 115km. and im going on 120km but we're both right beside each other

 

I bet even the digital speedometer is off. Both speedometers get their signal from Vehicle Speed Sensor, which is just a gear being turned and creating an electrical signal, not the most accurate device.

 

So you did this once before the fuse blew and you registered the exact same speed, then you did it again after replacing the fuse and it was off?

I'm just finding it hard to believe a new fuse would cause a speedometer inaccuracy.
Do you have stock sze tires & wheels? Does the Civic have stock size tires & wheels?

 

the civic was completely stock. what i see a big change is.. before the fuse was replaced.. my RPM was exactly a bit above 1 always. now the rpm is below the 1

 

The car is supposed to idle below 1000 RPM (Usually around 750 or so) once the car is warmed up. There is nothing wrong with the idle as you describe it. If it were always idling above 1000 RPM, then there would be something wrong with the car.

 

i guess i have to ask............which fuse did you replace ??
i have never seen a fuse effect that the speedo reads a bit different than actual car speed,
trust me do not waste your time or effort , all the speedo read a bit more ( 3-6 ) than what the car is actually going at .....
and as for the idle speed OOaccord was correct ,, once engine is warm it is suppose to be 700-750 rpm , if it only reads 500 it is a bit too low, need to raise idle just a bit , but than again, those gauges are not 100% accurate either but better than speedometer gauges ,,

 

i dont even know which fuse i replaced, i took all the fuses out and den i saw one burnt so i replaced it with a new one.