First off I'm a b5 guy so i have no experience on TT's. My brother has a 2000 Audi TT 1.8t 5 speed. It has 55,000 miles on the clock. He bought it early august 08. It had been siting in some rich guys garage for 3 years only started once in awhile. It was his midlife crisis car for a couple year's.
Now to the issue. I have had the car in my possession for about 1 month. During cold starts the idle sits around 1500 rpm to 1900 rpm. Then when i drive it below operating temperature's it has a bucking motion in the rpm range. I don't run it hard bellow operating temp nor do I by cheep gas, If that has anything to do with it. Thank's

 

is the check engine light (CEL) on?
i dont know what engines are in B5's but if its a 1.8t its 90% the same as the TT.
few things to look into: fuel filter, spark plugs, injectors, and timing belt. also check the air filter. start with the cheaper things...timing belts going to be the big one! but dont let this drag on! the timing belt can and will wreck your engine

 

Your Idle-RPMs seem pretty close to standard (I'm between 1k-1.2k cold start). Due to the vagueness of your description, it could be anything from dirty MAF, failing coil-pack in 4/5, fouled o2 sensor to rough engaging ball/spring MBC...

Could you be a little more specific about the conditions that create the problem?(EG:Between what RPMs is it most prevalent? What mods/upgrades have you applied to the car? Can you describe the "bucking" motion {like power loss?} in more depth?)

 

i have no Cel's. Air filter plugs and 4 new coil packs. For the bucking it does it between 2000 to 3500 for about .5 miles. then it goes away and runs just fine. as for b5's i really only deal with the 2.7t in the s4's and the 2.8. Don't know to much about the 1.8t

 

Wait until idle drops until you begin to drive. These turbo motors do not like moving when it is cold. It only takes a minute or two. Mine does the same thing. Just wait for the cold start idle to drop down to normal idle. No problems and its much better for the engine.

 

Do you have a boost gauge? If so, look and see if the "bucking" starts at the time you begin boosting. Mine does that, and I'm assuming it's a leak in my system. Been searching for it and finding new leaks for a bit now. The first major one I found was on the air injection pump, where the rivets had begun to break down and the pump was basically coming apart. Here's a link to a good write-up about it:

http://forums.audiworld.com/showthread.php?p=17195013

 

All the "bucking" I recieve under boost/load is due to my MBC... However, sometimes on frosty mornings (air is below 35'f) I will get pre-emptive dumps which feel like a moment of complete powerloss under load in 2nd gear. From what I've read this is symptomatic of the ko3 turbos and can lessened by simply accelerating through it. If you find a more distinct cause for the problem, please post it! I'm die'n to know a fix for it!!!

 

thanks Guys