Car is an '01 Audi TT, I have been experiencing an intermittent rough idle, with very occasional "Popping" sound from the exhaust... The car is also only putting out about 10 psi of boost, and the ECU is calling for roughly 15 psi... Not sure if the issues are related.
Readings taken during a quick drive after the car warmed up this afternoon showed the front 02 sensor resistance ~0.6-0.7 KOhms, and the post cat was 0.1-0.3 KOhms (No related trouble code). Voltages for the pre-cat were sporadic, from 0.125-0.895v.
Also of note, the internal resistance measurement for the pre cat sensor stopped displaying about 5 minutes into the ride, does this signify a fault, or may the heater have just turned off?
Lastly, when the car is shut off when idling roughly it has (Twice in 4 months) dieseled, or continued to run roughly with key off for ~4-10 seconds... Again, not sure if related, any insight is appreciated. Thanks!
The problem was a combination of bad primary O2 and a massive vacuum/boost leak coming from the brake booster line as it runs under the front portion of the intake manifold, blew as soon as pressurized (and no, it was not over pressurized) lean fuel trim caused check engine light 5 minutes before pressure test!