Had a mechanic replace the leaking power steering line and immediately following that I only get 8mpg. Prior to the repair I was getting 17mgp on average in the city. No codes and the mechanic said his computer showed the car was running rich? He said there were no codes so he wasn't sure what the issue was. He tightened my spark plugs he said were loose but that didn't make a difference. Spark plugs were changed recently and the car appears to be running fine. Has 125,000 miles on it and I just changed the oil. Was running fine before the replacement of the power steering line.

No sure where to start looking for the problem since there are no codes. Any ideas?

Very hard to imagine that kind of a mileage change with no change in the way the engine runs.

I'd be looking close at what the mech broke that runs close to the power steering line work. With a change like that you ALWAYS suspect the work done first.