rob8

My brother in law has a 1998 C280 which had been sitting idle for about 2 years. He wanted to get it back on the road as a second car and the battery was dead, wouldn't take a charge. Installed a new battery and it started right up and ran around the block just fine. He went away on vacation and three weeks later he started it again. Very rough idle, shaking and stepping on the gas didn't increase the rpm. Started it again and the throttle responded this time, but still idles very rough and almost stalls when not giving it gas. What is strange is that 3 weeks prior after 2 years sitting it ran like a champ. What could this be?
Rob