I have a 99 zx2 with a rough idle. Have replaced air filter and spark plugs. Would disconnecting negative. Battery cable make the car re-learn idle ? Also where is pcv valve located ? Any ideas ?

How is the distributor and rotor?
You sure the spark plug wires are okay or did you replace them too?

Disconnecting the battery would clear the adaptive strategy and erase any codes that were stored.

Another possibility is the MAF sensor which is located in the air inlet tube. Disconnect it's electrical connector and run the engine, if it runs better then the MAF sensor may be at fault.

If the problem is rough idle but better at higher rpm's then lack of fuel is not likely.

If the check engine light is not on then likely not a lean condition as it can compensate enough even when far enough out to set the light. Guess it could be a very longshot but without the light on I doubt it.

Check for intake leaks by spraying the runners with carb cleaner and see if it makes a difference.

Sorry this8384, but disconnecting a battery does reset the KAM (keep alive memory) on this vehicle, I've done it countless times and verified it with a scan tool that the learned values were reset along with erasing the DTC's. All that was left was a P1000 for not completing the OBDII monitor test.