Q: multiple codes and rough idling

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Car was fine and then had a loss of power, and the EPC, traction control and engine light came on. It idles rough (constantly going up and down). The codes that came up were P0171 P0222 P2637 P0638 and P0121. We've changed the spark plugs, New 100 & 428 relays, changed the small fuses, New fuel filter and replaced the throttle pedal (gas pedal) with no change. Could it be the throttle body or the MAF sensor? Bad wire? We're at a loss. When we changed the spark plugs there was oil on 3 of the 4 plugs.

My car has 90000 miles.
My car has an automatic 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. Once you’ve ensured that these things are fine you can begin to address the codes. While the P0171 is a lean mixture code, and may be brought on by air leaks among other things, three of the other codes are related to the throttle body. VW has a lot of throttle body issues and I have changed many of them on cars with less than a hundred thousand miles so it’s not unlikely that you need one. But I wouldn’t run out and buy one just yet. They are pretty expensive and usually not returnable. It would be more prudent to have the car diagnosed. By contacting YourMechanic, you can have a technician come out to your home or office to check out your Golf and let you know what it will take to solve the problem.

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