VAG-COM

Air Mass Meter problem diagnosis - CASE STUDY 1 (225 Coupe)

NOTE: all the information presented is personal opinion and presented in good faith, nothing on these pages is validated or endorsed by Audi and you should be aware that you could make changes that may disable features of your car.
Always note down the original setting of anything you do and if you are not confident with what you are doing then just don't do it.
YOU HAVE BEEN WARNED.

The owner had just had a timing belt changed and was feeling the car was not performing well, there were no serious signs like lumpy running or hesitation. Pulling the AMM plug for a drive would not have shown a noticeable difference.

A couple of logs were run to help diagnose the problem.

Block 002, 020, 115
Here we see that the Air Mass flow is down for a standard 225
Timing is being pulled a lot and early in the rev range
Command and actual boost are marginally degraded but this was not a vast amount.

Block 002, 032, 115
Here we see that the Air Mass flow is down for a standard 225 still
The Part Throttle Fuel Trim  has hit +ve figures of 12.5%
Command and actual boost are marginally degraded indicating the ecu intervening to a small level.

CONCLUSION:-
Although the car performed ok, The Fuel Trim showed the ecu attempting to compensate by asking the injectors to fire 12.5% over their average rating to compensate for lean running. The boost was slightly off and the Air mass output was quite low for a stock 225 TT.

We changed the Air Mass Meter for a new one.

Logging blocks 020 and 115

Timing being pulled much later and much less
Boost is looking healthier

Logging blocks 003, 032 and 115

The Air Mass Meter is providing much healthier readings
The Fuel Trim is easing up on the injectors and looking much better
Boost is higher overall.