I own an 2006 A4/B7 2.0T S-Line (will post pictures soon). Within the last few weeks I have had trouble with the engine idle. When stopped the engine idle becomes pretty rough--a noticeable shudder at varying tempo--occasionally slams into gear when starting from the stopped position. Never had this problem before.

I took onepoint8tee's advice and stopped by autozone to have my check engine light read. The following codes came up:

P0507: Idle Control Sys (RPM above expected)
P0171: Sys to Lean Bank 1
P0642: Sensor A Reference (Voltage CKT Low)
P2004: Intake Manifold (Runner Stuck Open)
P0171: System to Lean Bank

Any tech-savy folks out there offer advice/familiar with these codes? Thanks!

 

if it slams into gears i'm assuming you have an autotragic tranny, and it could be a bad solonoid thats cuasing a harsh downshift or upshift, system too lean could be cuased by a clogged fuel injector therefore the engine isn;t getting the right amount of fuel and the fuel pump can;t push out the gas through the clog, this would also prove more true at a low engine idle because you don;t have that high of a demand for fuel therefore the pump isn;t pushing hard enough, try STP's fuel injector cleaner, or any fuel injector cleaner gas additive on your next fill-up

if your voltage is low then consider a new battery....i think thats self explanitory

other then that i can't think of anything else that would cuase the problems your listing because anything else would seem to make it run rich rather then lean (i.e. a boost leak, or some other issue with the turbo)

good luck