Originally Posted by country_09
the P0300 code would cause your rough idle because you might not be running on all cylinders. Try changing sparks plugs and see what that does
Plugs for that motor are $13 each and very unlikely to be the cause of any problem at 55k miles. Dont just start throwing parts at it. That is not the way to fix anything.
P0300 is random missfire - code IS CAUSED by the rough idle because of another problem.
P0131 BANK 1 SENSOR CIRCUIT LOW VOLTS
P0171 Fuel Trim System Lean Bank 1
That leads me to belive you possibly just have a dead O2 sensor.(i belive that would be the drivers side o2 closest to the manifold) Does the rough idle seem to be rich? or has the gas milage gone down dramatically since you got it back?
-30* temps i could see the possibility of an o2 sensor heater dying on one of that age. being that its a LOW volt code, not and open circuit code - if you have a friend with a scanner that wont charge you $200 to read the streaming data and see what the 02's output voltage is to the ECU, then test the output lead with a volt meter to verify a bad sensor. They could have pinched a wire unknowingly replacing the trans but it cant be visably seen. Ive seen wires get cut without tearing the casing and one strand left conducting the power.
If it doesnt come back just figure it was a dirty MAF, ive had to clean mine at 54k miles.