Car runs fine when up to speed, rough ideling.

Tdi or gas engine? What size engine if gas?

Thomas

Vacuum leaks and or a dirty throttle body can cause idle issues.

Having a look at short term and long term fuel trim values with a scan tool can quickly indicate if a vacuum leak is a possibility.

Smoke testing the intake can find leaks that are not visible or audible.

Engine mounts can add to the roughness feel (excessive shaking of the engine), so those should be checked as well.

Thomas

Throttle bodies can be cleaned and an adaptation performed... sample from a Jetta I cleaned:

http://www.youtube.com/watch?v=OAfeBLENkfA&feature=plcp

Usually it is a low idle problem.... when the dirt gets too much in the throttle bore.

The high idle could be due to the throttle being faulty or the vacuum leaks I mentioned earlier.

Cleaning and adapting, as well as smoke checking is what I would start with if you came to my shop.

There are smoke testing clips on my site... search for smoke in the search bar to get some sample clips.

Thomas

I forgot to mention "check valves or one way valves" that can also cause idle / performance issues. The 1.8T engine has a number of them.

The check valves allow and block air flow when the engine is under turbo boost or not under boost.

Thomas

Sorry about the late reply. I was driving home.

I always perform the adaptation on new throttle bodies. As long as it is the correct one for the engine, it should be ok.

Don't buy any parts until they are confirmed to be bad!

I can only guess over the internet. If your mechanic is not familiar with VWs, check with a VW Specialty shop in your area.

Thomas