Q: My car rpm fluctuates slightly, during warm up and my temperature gauge also fluctuates intermittently.

asked by on October 11, 2016

I bought this car used, has been running fine, but I just discovered recently after about 2 months of driving, that it doesn't maintain a steady rpm at times (not always). Rpm will go between 1200 and 800 during starting engine at different times. Also, when I engaged the transmission (especially in "R"), vibration is observed on the steering wheel. Though improves in the "D" shift position. However, after a few hours driving, these conditions are suppressed. The noticeable observation again, during this warmed up state is that I could see that the temp gauge needle fluctuates between coldest and normal working temperature of the engine (though never exceeds this level). This condition does not occur on every driving, say about 35% of all driving time.

My car has 239000 miles.
My car has an automatic transmission.

Hi, thanks for writing in. My first impression when you described the vibration is that you may have a bad motor mount. When you put the car in Drive or Reverse, the engine shifts slightly. If the rubber in the mounts is tired, it will transfer the engine vibration to the chassis of the car. As for the temperature gauge issue, it could be that your car is not warming up. If the thermostat was sometimes sticking open, it would prevent the engine from coming up to operating temperature. If the engine is not warming up, the injection system will remain in a cold running mode, producing a high idle. The best way to check if this is the case is to use a handheld non-contact thermometer on the radiator and the engine, you should be able to see weather the engine is up to temp, or if it may be an instrumentation issue. Replacing the thermostat is relatively inexpensive and is a good first step on temperature related issues. You can contact Your Mechanic and have the thermostat replaced at your convenience.

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