speedometer sometimes work,at times it does not

Have you tried replacing the vss sensor (vehicle speed sensor)? It is located on the top part of the transmission. If you stand over the passenger side fender looking down into the engine bay you will see the intake, under that you will see the starter connected to the transmission. If you remove the intake arm from the intake manifold, and look straight down with a flash light you will see a sensor that is located on the transmission and held down by 2 10mm socket bolts. Remove the 2 bolts and twist the unit and pull the whole unit out the transmission, unplug the actual wire harness from the sensor and reverse instructions for reesemble. If all fails then you should look into replacing your gauge cluster. Good luck

Check the grounds for the dash panel. Also, unplug, clean and replug the various plugs leading from the dash panel to the rest of the car. If you notice any that seem sloppy (loose), have burned places, or are heavily corroded, replace them.

"I have this problem in a 1994 Prelude (94 and up have the EL lighted gauges). The speedo will be accurate, then BAMMO I'm going 140mph or 0mph. In my car, it appears to be heat sensitive. On a hot day with the car in the sun, the speedo goes wacky and the EL lighting and the odometer goes blank and quits working.

I replaced the VSS twice. No fix. I removed the cluster and replaced a capacitor or 2. No fix. I removed the cluster and pinched every single connector pin (take apart all green connectors 1 by 1) and still no fix.

My car has 111,020 miles on it. I got a used gauge cluster from a junkyard for $80 with 188,140 miles on it and it works fine. I had to get a different gauge. Now it works."

"Ray brown pretty much nailed it.

the only thing I would add, is if the car has a engine swap, then the people who swapped it might have damaged the sensor or installed one from another vehicle and just rigged it."

Check for corrosion on the connector. This is more common than most people think. Use a paper clip to clean off the connection points in the connector, since you've already replaced the VSS.

"I’ve been having this problem for a while after fixing my leaking distributor which probably damaged my starter. I just replaced the starter today, and it’s been firing up every time.

Before I replaced the starter, I replaced all the other components mentioned on other threads: the VSS, ignition switch wiring and even the battery.

After comparing the new starter with the original OEM starter, I found a chip near the spade connector which probably affected the connection (along with the oil that was dripping on it). This little connector probably was affecting the speedometer and inconsistent starting."