Today in the morning I tried to start my 1998 4cyl Accord but it had some difficulty on the first try it; was ok on the second go around. Later today it would not start at all, but would crank slowly to no avail.. I got a jump from my son and it started right up. My mechanic said it was the battery so I got a new one. My question is: I notice that the tachometer is all over the place in the 0 to 1000 range. Before this happened it would stay at 700-750 at idle. Is this occurring because the ECU is relearning my engine setup from the necessary sensors? I am not used to these sophisticated computerized cars, so please bear with me. Thanks

 

If the engine is actually holding a steady idle while the tach goes nuts, then look for wiring problems to the cluster. That won't have anything to do with 'relearning'.

But I suppose the idle speed is truly surging...
Do you get a check-engine light? Your mechanic should read what the error code is, or go to AutoZone & they'll read it. Get the code number, not just the guy's guess for what caused it. You got a couple things that work together to control idle, like the IAC valve on the intake manifold...

Oh yeah - look for vacuum leaks, too.

 

My car is back to normal today. So I can not explain the tach problem, but it is right on the money today. Thanks for the reply.