at idle rpm fluctuate? called knock?

[nwgtr]

at first my car studders at wot but now it gone because i replaced the spark plugs.

Sometimes i notice that i start my car and at idle. the rpm would fluctuate between 1k and 1.5k

then goes away, and sometimes happen between couple seconds apart.

and the sound is similar to the bass on a sound system.

thump and the rpm goes up .5k and back down.

could the pcv valve, wires, coil pack or manifold crack cause this?

 

[blackbyrd]

http://www.dsm.org/how-tos/tttt/tttt3.html
http://www.vfaq.com/mods/wayback/BradBauer/engine/surge.html

 

[nwgtr]

thx buddy, so it's called idle surge. going to read it and see if it helps

 

[blackbyrd]

Good luck, report back if those sites don't help, we'll try to help you out.
You could do a intake leak test too:
http://www.vfaq.com/mods/ICtester.html