i just noticed (i think it just started to do this for about 3 weeks now)... at idle.. my car dips and rises in RPMS every few seconds. it will be at 700 and then it will dip down to 600 and then rise up to 800. my exhaust makes a puffing noise too.. and you can feel vibrations while sitting in the car too when it does that. it only does it on a warm engine too... im thinking maybe its just my exhaust setup or maybe its something more serious? bad fuel injector maybe? it might not even be a problem.. maybe its normal? to be honest.. i kinda like the sound of it.. however... i wanna know if something is messed up.