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Q: Engine shakes when heat is on

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I have a 2001 PT Cruiser. Engine shakes/vibrates loudly for like 2-3 seconds at a time on cold start only when I turn on the heat and let the car idle in park position. Does this for a while until car is "warmed up". Doesn't do it if I leave the heat off while letting it idle in park position on cold start. What can be the cause of this? Thanks.

My car has 106000 miles.
My car has an automatic transmission.

Hi There, This may potentially be a result of the change in heat in the coolant that results when turning on the heater while the car is still warming up. As you may know, when the car is first started when cold, the coolant temperature sensor reads the temperature of the coolant and relays this information to the ECU. Te ECU uses this information to make adjustments to the air/fuel ratio (adding more fuel) to the fuel supply as the engine requires more fuel to run when the engine is cold due to the difference in air density at colder temperatures. I would suggest having a professional from YourMechanic come to your location to take a look at your vehicle.

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