1999 Ford Mustang Engine idles rough! Codes P0171 and P0174

1999 FORD MUSTANG
98,000 MILES • 6 CYL • 2WD • MANUAL
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JMOORE0180
  • MEMBER
  • 15 POSTS
The engine idle very poor, when coming to a stop, the rpms die to around 300, then go up and down making a sucking sound from air filter box. Ive replaced the Mass Air Flow Sensor, and the Idle Air Control Valve. Im not sure whats doing this... Please help!
Oct 18, 2010 at 4:39 PM
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JIS001
  • ✓Experienced Mechanic
  • 3,412 POSTS
Fuel trim codes in both banks with a rough idle indicates you have a bad vacuum leak. The easiest way to find the leak is by smoking the intake system. But from my little experiance I have, I would be looking for a collapsed PCV Hose. Look for the PCV Valve on your vehicle. Looking at the emissions sticker under the hood will tell you where the location is. Once you find the PCV Valve, inspect the hose and feel it. While the vehicle is idling wiggle the vacuum hose and you should hear the hiss get loader or go away. If you do you have found the problem. Replace the hose with the valve. This will be most likely a dealer item. Good luck and let me know what you find with the hose.
Oct 18, 2010 at 4:49 PM
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