Idle fluctuates with a.c. on

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15/02/2021 3:26 pm

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Idle fluctuates

I have a 2010 Mazda 3 Automatic trans. 2.5 liter 234,000 miles. I love the car , it uses no oil. The idle fluctuates between about 600 rpm and 1100 rpm. It only happen with the a.c. on. I changed the spark plugs with NGK brand , fuel cap from Mazda , an $82. Mags air flow sensor from Rock Auto. With the new air flow sensor the check engine light turned off and the idle seemed to be fixed but 10 minutes later the idle started fluctuating again and the engine light was on. I went to a shop to see if maybe my a.c. needed more coolant / Freon ; they said it was fine; it wouldn’t get any colder. They thought it might be an issue with the idle control regulator. The codes are PO172 ( system too rich) PO101 (Mass or volume Air flow circuit)

Any ideas??

BluepillMazda

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3 Answers

15/02/2021 3:38 pm

you could try a fuel injector cleaning, and make sure air filter is clean

MountainManJoe

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15/02/2021 5:47 pm

Did you buy an OEM MAF sensor? I can't even count how many times this problem is caused by faulty cheap aftermarket sensors.

MountainManJoe

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He said he put on a new MAG (read that MAF)sensor from Autozone. Probably a low price aftermarket part, not OEM.

By Doc 15/02/2021 6:01 pm

Was about to point this out! Odds are he just needs an OEM MAF sensor.

By InThrustWeTrust 15/02/2021 6:08 pm

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15/02/2021 4:36 pm

Look at the IAC. When the AC is turned on, an solenoid raises the idle to compensate for the compressor load. I would bet it was the IAC or TPS.

Doc

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I don't think it has an IAC. Modern engines regulate idle by controlling the throttle.

By MountainManJoe 15/02/2021 4:46 pm

Thanks, Joe- It sounds like the idle rpm is not getting raised when the AC compressor is on. Is this part of the ECU program?

By Doc 15/02/2021 5:22 pm

Yes, but I don't think his idle is too low. It sounds to me like the engine is running poorly on its own, and the AC is making it worse and more noticeable.

By MountainManJoe 15/02/2021 5:46 pm