has large and small evap emissions codes in computer
40-45 mph car jerks badly stomp on gas straightens up has large and small leak on 2000 Ford Mustang
Evap codes will have no relation to how engine runs...probaly a differant issue causing jerking....more like a ignition missfire more likely.
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At 40-45 mph this vehicle may exhibit such a jerk when it is time for a tune up. At this cruising speed egr flow is present and can overwhelm a weak ignition system causing such a symptom. Don't skimp on parts. Do a major tune up. Check the fuel filler neck for cracks or excessive rust. Take off the gas cap and check in the filler neck. Also check gasket on gas cap for cracks.