I have a 2000 Mercedes Kompressor that sat outside all winter. I started it two days ago after replacing the battery but the car only starts and idles, when I press the gas pedal down nothing happens it just stays idling with no acceleration. I put a can of Heat and some fuel injector cleaner in the gas tank, but it is still doing the same thing. Any suggestions?

Check the Accelerator Pedal Sensor....

I have the exact same car and had (past tense) the exact same problem, with a little more hassle than you had. The stock battery (mounted in the trunk as you know...) COMPLETELY drained/died during a very cold winter night and the electric trunk lock would not operate (of course) So, I went to use the key and it was so cold that the key broke off in the trunk lock. Ended up drilling out the trunk lock and screw-driver'd the trunk open. Long story short, I got a new battery (huge suckers aren't they?!?!?) and the car started and idle'd just fine. Upon acceleration however, I'd have done better to stick my feet out and push the car along like the Flintstones did. Come to find out, the computer resets itself when the battery is changed so it needs to "re-learn" the fuel/air mixture ratio (and some other stuff I can't remember) depending on your climate, temperature, altitude, etc. It took me about 40 miles of starting, stopping, accelerating, highway cruising, etc for it to run properly. The first 10 miles are the worst and it does get worse before it gets better (but it does get better!) So just nurse it along for a while and you'll be fine. And, good luck with the radio code... The stereo resets itself also and you need to type in a code on the radio to get it to work again as well. (dealer has the code if you give him your VIN # or you can take the radio out and the 5 digit code is printed on the top of the radio. Good luck!

go on youtube there are the steps there to relearning your engine to start and operate normal ...