Hey,

I have a 95 Audi 90 that has a low idle problem. It failed emissions because of it. There is no power loss or hesitation it just can't keep a Consistent idle it's below 900 rpms and above 700.

 

While a low and variable idle can be a host of things, a vacuum leak can be one, and I have seen that on my '95 Cab. Assuming a 12V engine, remove the plastic shield and while at idle, move the vacuum lines and listen for an obvious hiss and a drop in idle. Pay particular attention to the tubes and hoses on the drivers side inboard of the valve cover that have the 90 degree bends and plastic check valves. I have had each one of the 90 degree rubber hoses split and dump vacuum, and one check valve no longer operate as a check valve - i.e. the diaphram disintegrated. So if it has happened to me, it can happen to you.