P0170 MAZDA -

Question

Man this cars runs great except when the rpms drops low and it will sputter. I changed all the sensors fuel and oxegen plus changed air filters I got a tune up what else could it be. I work on this car myself do not have money to pay a mechanic. The check engine light comes on and i go and get checked and it is always p0170.

Answer 1

I'm in the same situation. I cannot afford to have someone else do it for me. But why just replace all those parts when TESTING them should be the first action? Unless your time is far more precious than money, you probably spent a lot of money that you did not need to on all those parts. Testing procedures should be available for your car to determine bad components with a simple multi-meter or $100 scantool.

Have you cleaned the throttle valve? It's worth a try if the butterfly valve may be a little sticky.

The first thing the diagnostic procedure states for the P0170 (and also P0171 & P0172) code would be to check for intake vacuum leaks, and then look for exhaust leaks (check gaskets)... both can cause misleading O2 sensor readings that the computer compensates for, and the fuel trim reaches it's compensation limits or is beyond specs.

This computer compensation of the fuel injector "on-time" is like manually cranking up the fuel mixture screw towards "rich" on a carburetor to compensate for a vacuum leak. The scantool should show the short term trim conditions. If readings are widely varying up & down, it indicates a compensation problem.

The actual names and use of these parts may vary... Test the fuel pressure and regulator function. Check the manifold pressure sensor & connector. Check coolant temperature sensor. Check Intake Air Temperature sensor (if applicable). Check the fuel tank pressure sensor (if applicable). Also check the Vapor Canister for clogging and bad EVAP hoses. Check the Canister or Vapor Purge Solenoid(s) or Valves. Check fuel tank vent system (or valve if applicable). Clean the gas cap seal or replace cap. Test for water in fuel or alcohol separation (fill glass jar and let sit a day, look for separation).

I hope this helps. I'm chasing down the same code on my 2000 Subaru Outback, but I do not have driveability issues. My code is commonly occuring within a few miles after refueling. I've completed all the diagnostic test procedures on my car and all results were okay. So now I'm chasing other possibilities in the vapor recirculation system that may mimic the condition.