Warm garage 30 degree day outside,started cold truck to do some errands. Backed out of garage and stopped to shut door,truck did a RPM stumble and recovered and rpms went up some. Set check engine light in dash. A small deposit of black crud by tailpipe(new white snow on ground). Ran errands cycled ignition a few times and engine light went off. Any help appreciated. Thanks !999 275 RV va rasp