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Q: high rpm when starting car, then idles very rough. Also lack of power accelerating at times while driving

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At random when starting car, engine revs high to 2000 rpm several times, then drops to 1000 and idles very rough. while driving at times either on highway or side road, the car goes into limp mode and pressing accelerator gets no response. Starting happening after driving across country in summer after about 8,000 miles. engine light was already on at start of trip. ETM was replaced and software upgraded in july 2015 at volvo dealer by previous owner. After towing to mechanic, car working fine, who then referred to volvo dealer Now at volvo dealer for several days, they are unable to get the car to replicate symptoms above, told me they have to keep trying until symptoms show in order to locate problem. Fault codes are 951F, Accelerator pedal position sensor; 903F Throttle position;902B Communication with throttle unit faulty signal; 2210 rear heated O2 sensor. Not sure where to go from here, thank you for your time.

My car has 110716 miles.
My car has an automatic transmission.

A: These codes all point to the operation of t...

These codes all point to the operation of the throttle position sensor. The throttle position sensor is a sensor used to monitor the throttle position relative to your foot on the gas pedal. The sensor is usually located on the butterfly spindle/shaft so that it can directly monitor the position of the throttle. The ECU then makes the direction to supply more or less fuel to the motor. When this sensor is not working properly, this can cause intermittent responses when pressing the gas pedal. The last code related to the O2 sensor relates to the oxygen sensor behind the catalytic converter which monitors the exhaust gases after they leave the catalytic converter. This essentially reports whether or not the catalytic converter has done it's job correctly or not. When this is faulty, this may cause inaccurate signals to be relayed to the ECU which then causes inaccurate amounts of fuel to be supplied to the motor causing the rough idling and poor running condition you describe.

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