Q: trying to figure out misfire or fuel system problem

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i have a 3rd engine mustang with around 140000k I believe and its losing power when I accelerate. It happens in all gears and at all speeds. And sometimes leaves me with a rough idle. It shakes and only seems to have maybe 30-40% of its normal power. It shakes and sputters I can feel it in the steering wheel. It also leaves an unburnt fuel smell when I get out. Sometimes puts out white smoke out the exhaust. Not heavy just a light amount. Sometimes while it is sputtering it will act like it caught the gear and will pick up like normal when I accelerate but after I let go of the pedal it sputters again. It will only happen maybe 1 out of every 50 times I press the pedal. I changed 7 of 8 spark plugs (a bolt for the cool was rounded off didn't have the socket for it) and no change. I turned off the fuel system from the trunk and let it die then turned it back on and that seemed to fix it! But then today (about 2 days later) it starts happening again.

My car has 140000 miles.
My car has an automatic transmission.

When the problem is happening you would need to have fuel pressure checked to see if the pressure is low and if the filter and pump needs to be replaced. If you have an oil bath type of air filter then you may have a contaminated mass airflow sensor and you may need to replace it or try cleaning it first. Also, use a paper style filter instead. If you need some help with this, consider YourMechanic, as a certified technician can run these checks and diagnose your misfiring firsthand.

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