01 TT CEL and EPS light
 

For awhile the check engine light has been coming on for a week, going off for 2 days then coming back again. I changed the spark plugs which didn't help. It is now staying on permanently and at times the eps light will come on as well. I read that the MAF sensor plays these tricks so I went ahead and cleaned it -- no change. I installed a new MAF sensor, the CEL went out for a few days but now it's back on again and is still accompanied by the eps light at times.

- The exhaust smells rich.
- It's rare but the throttle has very very slight hesitation

I will get the codes read and posted tomorrow. I think my next step would be o2 sensors and/or new cat. Thoughts?

Until you run a proper diagnostic scan with VAG or Ross-Tech software; all you would be doing (and have been doing) is throwing money around at random. You could have an air or vacuum leak anywhere on the engine or emmision system causing a fault. A brake light switch can cause an ESP error. EPC errors can be caused by the pedal assembly, throttle body and anything in between.

The list goes on. Generic diagnostic scanners will not read VW/Audi specific message identifiers.

Thanks Bally, I've been pushing off on inevitably buying a vag com. It's ordered. I'll repost when I have some answers.

You will be glad you bought it. Trust hundreds of us on these threads.

you could go to autozone or advance auto and have the codes read.
without knowing what the codes are, you're just shooting blanks in the dark....

Looks as though changing out the MAF sensor fixed my problem. CEL has gone off and has not come on for 5 days now. Longest stretch of time it's been off in months. Best guess I have is that it took awhile to recalibrate?

Those generic scan tools will read SAE codes but not VW/Audi specific message identifiers.