I'm hoping someone can tell me the logic behind my care revs dropping in cold weather when I turn on the heater. I have a 2002, 130 BHP 1.9TDI A6.
The revs will drop from ~1000rpm to 800rpm and then back again. It will do this every 10 - 15 seconds in an irritating yet consistent pattern. The second I turn off the heater it stops. It doesn't happen once the engine is warm enough. What could cause the heater to drain the engine's power like that ? The only thing that I know to be wrong with the car is that the dash instrument panel is on its last legs, it reads 115 degrees C as opposed to the usual 90 and also the fuel guage goes nicely beyond the 100% line when the tank is full. I've had the engine read for faults and nothing shows up. The engine reads 90 degrees C even though the dash gauge reads higher. I did replace the thermostat recently but this annoying loss of revs in cold weather persists when the heater is on. Any thoughts would be much appreciated. Thanks.