My Passat Estate 1.8 manual (non-turbo) year=2000 with 56000 miles if failing the test on emissions.
Test Results
Low idle CO 0.05% (Allowed 0.5%)
HC 9ppm

High idle Lambda 1.11 (Allowed 1.00+- 0.03)
CO 0.01% (Allowed 0.30%)
HC 9ppm (Allowed 200ppm)

Got the car checked and new Lambda sensor fitted which gave the following result.

Low idle (860rpm)
CO 3.15% (Allowed .5%)

High Idle
Lambda 1.029 (Allowed 1.03)

This was after a small leak in the exhaust was fixed.

New Lambda sensor (another one)

Two new test runs:

Low idle CO 3.32%
High Idle Lambda 1.090

2nd run
Low idle CO 3.23
High idle Lambda 1.120

All other figures OK.

Mechanic says he can do no more - take it to someone else.

Help.

I have owned the car from new so mileage is correct.