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Q: Starting and idling problems

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i recently replaced my catalytic converter and a day later my car wouldn't start and 2 codes pop up one was for the throttle position censor and the idle air control valve i replace both and the check engine light went off but my car only starts when i hold the gas pedal to the floor then when it starts i let go of the gas and it dies instantly . sometimes it will stay running but idols really rough

My car has 211000 miles.
My car has an automatic transmission.

This may be a result of a faulty oxygen sensor. As you may know the [oxygen sensors]((https://www.yourmechanic.com/services/oxygen-sensor-replacement) which are part of your emissions system read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car’s ECU which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on. Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors. Too little oxygen may be present in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors or a clogged catalytic converter. When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine. I would suggest having an expert from Your Mechanic come to your home to diagnose your emissions system.

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