If you can eliminate the fuel and air filter as the cause then the next thing I would do is check the Throttle Position Sensor in the Throttle Body. Some times the shaft that the TPS is connected to gets worn out. I would also remove and clean the Idle Air Control sensor in the TB. The IAC can get real dirty along with the bore it sits in. Remove it and clean it with some type of liquid like carb cleaner and fine steel wool. Make sure you clean the bore in the TB also.
I like to check all the stuff that costs nothing to check first...
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