93 altima GXE idle problem

1st of all, i just wanted to say that im happy that i finally found a decent forum!

2nd, my problem with my altima is that it idles so rough that it shakes the car. when i first start up, it doesnt do it, but after 10- 15 seconds, it starts misbehaving, when im in park, its not so bad. when im in drive, its at its worst. i dont have any lag when i accelerate, and i changed the plugs, new motor mounts, distributor and rotor, though i didnt get the timing done on it. now, im a bit ignorant to this car still, and i think it could be the Idle Speed Control Valve... also, its idleing at about 750 - 1000, and the onlt time its not so bad is in park. it doesnt die out, and it has trouble starting about 1 in 5 times. any ideas?

Correct ignition timing is very important because it provides the referance point that the computer uses to issue adjustment instructions. 10-15 seconds may be the time that it takes for the computer to take control from the preset fuel and timing instructions used when the engine first starts. You could buy an inexpensive timing light for the same dollars as it will cost to pay a tech to set your timing. Then you can practice as often as you like and you will know for yourself that the ignition timing is correct. Follow the instructions in the repair manual. Once the timing is set, it doesn't change. If your engine still vibrates after setting the timing, perform all the cleaning and tests for the idle control system and PCV.

Correct ignition timing is very important because it provides the referance point that the computer uses to issue adjustment instructions. 10-15 seconds may be the time that it takes for the computer to take control from the preset fuel and timing instructions used when the engine first starts. You could buy an inexpensive timing light for the same dollars as it will cost to pay a tech to set your timing. Then you can practice as often as you like and you will know for yourself that the ignition timing is correct. Follow the instructions in the repair manual. Once the timing is set, it doesn't change. If your engine still vibrates after setting the timing, perform all the cleaning and tests for the idle control system and PCV.

where can i find the cleaning and test guide for this car? i dont have the manual, but i have access to a Haynes manual, and, sorry for my ignorance, what is the PCV?