My 92 Honda Civic's speedometer read 0 when I was going at least 20 mph. Then it would suddenly jump and read correctly. Then when I was on the freeway going 65 mph, it read 0 again. Took it to a mechanic who could not duplicate the problem. Got the oil chgd, intermediate svc, new timing belt, camshaft, oil seals, water pump, auto transmission svc (major), adjusted rear brakes 4 days ago. Tonight, ck engine came on while going down a windy hill. Parked on level ground, waited 5 minutes, then restarted engine. No ck engine light. Drove on freeway going 65 mph, but the speedometer read 0 again. Jumped around again. Is this bad for my engine? How can I read the engine codes (is that available on my 92 Civic)? What could it be?

Here's how to check for codes:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-6.html#post832012

My guess is that the Variable Speed Sensor (VSS) is bad. It's located on top of the transmission, close to the firewall. Easy to replace.