I had a tune up about 3,000 miles ago, and I changed my spark plugs myself about 2,000 miles ago, and my ignition cables about 20 miles ago. My car was havng problems idling and running @ low gears, it felt like it was going to stall. I changed the sparkplugs and it ran fine. I drove from VA to CT and the car ran fine. Now that I'm home I let the car sit for a few days because I had nowhere to go and then it started to have problems idling and running at low gears again. (It was rough in streets but fine on highways). I changed the oil this morning and the ignition cables but it's still running rough and now it's running rough on the highway. What can I do?