Took my wife's MY95 WRX to Surrey Rolling Road on Saturday for a pre mod baseline and health check run. The old girl managed a respectable 255 bhp which for a 13 year old car with only a decat is not too shabby.

One problem that was highlighted was a slighty lean AFR for an otherwise standard car.

On boost the AFR was 11 when we would normally expect 10 on an OEM Z4 (ie rich as standard)

Although the 11 AFR is fine and stable you would normally only see this on a tuned car not an OEM ECU.

While not in any immediate danger i was advised that the MAF was probably to blame and could be replaced to solve the issue. After this discussion someone else mentioned that the MAF may well respond to a good clean.

After your thoughts really, anyone have an idea of the price of a green label MAF? I have seen lots of websites selling the later MAFs but not the older ones as am i correct in thinking that the older variant are slightly more robust normally?

Can the MAF be cleaned, if so how - and if i did clean it is there anyway other than another RR session to prove that it is working correctly?