Its been real cold for the past 2-3 days with temperatures at 0F-5F. I noticed first that the heating was not coming on when I started the car in the morning, then, within 10 minutes after I hit the highway, the car started chugging when I pressed the accelerator. When the accelerator was slightly depressed, there was no problem. Then I stopped the car and turned the ignition off. When I restarted the car, it seemed to run fine, except no heating still.... Can you please help ???