'98 A8 4.2 TPS - and Idle issues
 

I have had my Audi for 2 years. It has has some front end damage that i am still working on fixing. (bumper, tie rods, upper links ect) but when it started having issues with shifting I got nervous. My brother is my usual mechanic (hes Certified Audi), but he said he didnt do transmissions, so I took it somewhere else. They charged me 80 bucks for a diagnostic to find out that its the Throttle Position sensor...well after he gets it all put back together the car throws trouble code P1509 Idle system electronic malfunction. Now it wont even run! It starts and immediately dies. I can hold the gas for about 2 minutes and it will stay running.

Is this a common side effect of the TPS going bad???

I coulda lived with the crazy surging and confused shifting for a little while. 300 bucks is a lot and I dont need this to start nickel and diming me. The car ran so smoothly before this aside from the surging, and confused shifting...I dont think there is much else wrong here...but I am not ready to start throwing thousands of dollars at this car. Any ideas?

Re: '98 A8 4.2 TPS - and Idle issues
 

nopey. No ides. Can say that D2A8s have tranny design problems. Audi won't admit it, but I've seen more than a dozen D2A8s with same tranny propblems. One prob is piston design on reverse. Pressure gets too high, blows spring and voila! no reverse. Redesign of piston, was required to permanently fix problem. F1 guys in Montreal figured this one out a few years ago. Forward gears is another flaw. The design of clutch plates, I think was too thin so they shattered/split. I saw mine when it was all apart. Audi replacement parts were totally redesigned and thicker, etc. Slippage may be sign of forward gears going, same as mine did a few years ago. It can get quite expensive. Better decide now before throwing a lot of $$$ into such an old car, although if the rest of it is good or very good, you might consider spending a bit more and tuning it up. Car will never rust, frame will always be strong and car is very safe and provides a smooth solid ride - with lots of space for 5 plus luggage. Tough call.

Re: '98 A8 4.2 TPS - and Idle issues
 

P1509 is an idle air control circuit fault, not uncommon.

If you're expecting a generic scan tool to solve your issue, stop there and find a factory level tool like the VCDS and look at it again.
Complete a throttle adaptation after the faults are deleted and test again.

If you're planning on aftermarket replacement parts then What You See Is What You Get.