Manifold Heater 12 VoltManifold Heater 12 Volt Keeping your intake manifold warm is the job of the preheat tubes from the exhaust. Often these get plugged up with carbon. This can be checked by removing the exhaust and blowing into the preheating tube with compressed air. If air does not pass through, the tube is blocked and the manifold cannot transmit exhaust heat properly. You can try to rid the pipe of carbon deposits again, but often this does not work. The simplest