Q: p0175

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I have a 200y Chevtahoehat we bought 2 months ago. Since we have owned it's had a very rough idle once it's warm. We have replaced the spark plugs, the spark plug wires, the MAF , had the injectors and throttle body cleaned 2x and had it checked for vacuum leaks and replaced the gas cap.t. The last round of codes were P0175,P0455,P0300,P0307. We are at a loss. I love this car but I cannot spend shops prices anymore. Looking for advice from where to go from here if at all possible.

My car has 164000 miles.
My car has an automatic transmission.

Hi There, This may not be as bad as it appears to be as these codes may all be related. Code P0175 relates to a rich fuel condition (too little oxygen in the exhaust) which may be caused by a few different things such as a faulty mass air flow sensor, a fuel pressure problem or a faulty oxygen sensor.

Code P0455 relates to the evaporative emissions control system which as you know, controls the vapors in the fuel tank. Your initial replacement of the fuel tank cap was a good start, but this points to a system leak which may be what is causing the rich fuel condition indicated above. Your car has a small purge valve with a purge solenoid in the Evaporative Emissions system that controls the venting of fumes from the fuel tank as these fumes build up inside, particularly when you are refueling the car with gas. The EVAP system prevents fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system collects and temporarily stores the fuel vapors in the charcoal canister. The charcoal canister is filled with activated carbon pellets that can absorb the fuel vapors. When the engine is running, the fuel vapors are purged from the canister and burned in the engine. The vent control valve (solenoid) controls the flow of outside air in and out of the charcoal canister. The vent valve is controlled by the engine computer (PCM). Normally the vent valve is open. It closes when the engine computer tests the EVAP system for leaks. If a leak in the EVAP system is detected, the Check Engine light will illuminate on the dash and the trouble code related to the problem will be stored in the engine computer. When an air leak is present in the EVAP system, the MAP sensor will not be able to determine the air density, and the MAF sensor will not be able to determine the volume of air, entering the engine correctly. This will lead to an over fueling situation or an under fueling situation depending on the size of the air leak and engine operating speeds and load. This may eventually lead to catalytic converter problems as well as misfiring problems. I would recommend having an expert from Your Mechanic come to your location to diagnose and inspect your vehicle.

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