When the car is idling in neutral or with clutch fully engaged the engine sputters, kind of revs and then drops. It doesn't die, and when the accelerator is engaged even a little, or I have the car in any gear, there are no issues. Also having the A/C on makes it sputter significantly less, sometimes not at all.
My car has 227000 miles.
My car has a manual transmission.
The first thing to check for in any drivability problem is air leaks. Any air that gets into the engine without being measured will lean out the system and cause problems. Look at all the rubber hoses and boots under the hood to be sure they are well connected and in good condition. After you’ve established that there are no air leaks, I would begin to suspect the throttle body. The throttle motor makes fine adjustments to control the idle speed, and it may have developed some crud around the valve so that it is not letting enough air through in idle position. Turning on the AC kicks the idle up just a hair so it smooths out. It might be possible to clean the throttle body rather than replacing it. Contact YourMechanic to have a technician come out to your home or office to check out your rough idling Mazda and recommend a solution.
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