Go get it scanned, it's free. The original codes you have aren't correct.

 

No the codes are write, they were just written down incorrectly, it's easy to match them up if you use the chart. Either way, if those codes are correct, what do you suggest I do?

 

P0442 - yeah that one is usually the fuel cap as you stated.

P1128 - Long Term Trim Mult, Bank 1 System too lean. Do you have a V6 or 1.8t? on the V6, bank 1 = passenger side.

How many miles do you have? If you above 80k or so, I would replace the pre-cat O2 sensors.

 

yes, it is the 1.8t, with about 80,000

 

I would def start by replacing the pre-cat O2 sensor. You'll get better fuel mileage too!

 

Do you think that could actually affect the idle though? Should I replace the fuel filter also? Do you know how to change it? It looks like the whole gas tank needs to come out.

 

Yes the O2 sensors CAN effect idle. When one of mine went bad the car would shudder at cruising speeds and would not idle very good. Here's a tech writeup on the fuel filter change:

http://www.audiworld.com/tech/eng49.shtml

 

I have a bad o2 sensor right now. My idle is jumpy when I slow down to pull into my garage,
Need to replace in a week or so.

 

At 80K mi. , you should replace the spark plugs and air filter.

 

You have a vacuum leak somewhere.