Having the same problem with a 1998 Honda Accord, V-6, if you've got a trouble code then follow that trail, TPS (throttle positioning sensor), IAC (idle air control valve) and MAP sensor (mass air flow), will generally post a code to the ECM, if not then look for vaccum line leakage,(motor mount system may be vac operated and the lines can easily get loosened). The last possible suspect would be the O2 sensor, you've probably got 2 of them, the upper one(closest to the engine) tends to get more heat abuse. (Look for the simple fix first)
You need to have the main relay replaced. I did that with my 1992 accord. ask around if you don't believe me. good luck. ro
On throttle body. It lets in extra air at idle when engine cold and throttle blade is closed.
It is broken. AC's usually blow cold air.
Have the vehicle scanned for codes. The codes will help determine the why.
it turns off and on depending on how hot or cold you are running its all on your thermostat
A mix of 50% clean water and 50% antifreeze is recommended in most climates. Add only when engine is cold.
possibly a leak in cooling system
15 hp
Honda tachometers are notoriously sticky. Almost every one that I've seen does what you describe. Yeah, but what's his problem? I have a '92 Prelude manual tran. with maybe the same problem: tach. fluctuates upon deceleration, but no noticeable actual change in engine rpm's. Acts like a loose wire or connection. Also doesn't happen when engine is cold, but once warm starts fluctuating for about 20 minutes...then goes away. Engine seems to run fine all of this time, but it's distracting.
Needs a recharge
Our 1997 Honda accord has had the same problem two times. Get the coolant recharged at your mechanic. We have had no problems for several years afterward.
The Honda Accord of 1998, just as any car in a frosty/cold morning, shakes because the engine is trying to warm itself up. Any car has gaps like the tiny edges between the bonnet and bodywork that can let the cold/ frost/snow in. A car's engine doesn't shake in '10 mintues' (some cars less/ some cars more) because then it's warm enough to not need a jig from the internal heater.