Imaging through class will definately cause you problems. I was mucking around with my SAC the other day and cursing 'cos I couldn't get a sharp image. Then realised I was shooting through a closed sliding glass door.
How far away was the car from your scope? You weren't within the minimum focusing distance were you? You may also have thermal currents inside the telescope to contend with as well. Definately get the IR filter. My experinces over the past week or so have convinced to me of the value of having one, though I haven't tested it out on a Toucam yet.