Okay, the check engine light came on in my 2002 xg with 87,000 miles. All maintenance was completed prior to this without any pre existing problems. The code was for P0320, ignition/distributor speed input circuit and primary/secondary ignition coil circuit malfunction. After the light came on I did not notice any performance issues but whats weird is that my rpm tach gauge would shoot down to zero and then back to where it should be at random without affecting the performance. I was told by the shop I brought it to that i needed new ignition coils and to replace the plugs and wires. I checked the coils and the voltage was within the factory parameters in my shop book and all three read pretty much identical. I did replace the plugs and wires with premium wires and iridium plugs which I noticed improvement in mileage and performance. I disconnected the battery and reconnected it to try and clear the code which it did and drove it for a day letting it idle, run at highway speed and rapid acceleration without triggering the check engine light. The tach gauge did the same thing once after i reconnected the battery and the light did not come on until I was waiting for a train and put it into park which it popped up immediately afterwards. The tach has done that acouple times since but always corrects itself soon after. Any help would be greatly appreciated because I am lost at this point on what else it could be since I do not notice any performance issues.

 

Since the tach is going out on you, it sounds like it's a sensor. The tachometer is driven by the "Ignition Failure Sensor" which is pretty easy to get to. It's on top of the engine right next to the air cleaner.