Hi everyone. Im new here, mainly to find out what is wrong with my father's caddy. At a stop light, when you take your foot off the brake even the slightest bit, the engine starts "chug-chug-chug" and with each "chug" the car moves forward. The idle sounds like crap, but he did just have a tune up not too long ago. Any idea's as to what the chugging problem is? Thanks for any and all help.