slight pulse at warm idle

[colinmitchell111]

i noticed when my truck idles when its up to temp it has a slight pulse like maybe 50 rpm. when its cold it does not do this. it is just enough to see the needle on the tach move a little bit and you can hear the engine change note. it pulses about every 2-3 seconds. i dont think this is a big deal but do you guys have any idea what causes this?

[Tyler]

mine does it every now and then. No bid deal to me.