My 2000TL with 85,000 miles was throwing the P0170 & P0171 codes. After about 2 weeks of seeing the CEL, I tried Chevron's Techron fuel system cleaner (with an almost empty tank) and 12 gallons of premium. I ran the car for about 15 minutes, flooring it a couple of times.

I parked the car, and when I started it in an hour or so, amazingly, the CEL was out and so far has stayed out.

I usually use mid range gas (89 octane), so maybe now I will start using premium on occasion.

 

the TL requires 91 or higher, if 93/94 is what they sell as premium in your area- thats what you use
Its really made to run on 94 but will accept 91,,so you are hurting the entire combustion process
Countless threads with live scanner readouts prove the few cents differance in gas price is worth it in the long run- it says 91 or higher right on the gas cap!!

You might try Seafoam, DIY - it restores things to like new
at 85 you need new NGK Iridiums too
have you done the 105 service yet--well past its 7 year deadline

 

You are also ready for EGR port cleaning by removing intake manifold
See DIY section

those codes are O2 sensor right?