Does anyony know what the correct voltage reading would be when my 1998 subaru impreza turbo is idling at the mass air flow sensor when you have a diagnostics computer is plugged in, mine is reading 3.1volts and did change to 2.7volts for a second, having problems with the mafs, old one was making car judder at higher revs, the second hand one i bought is keep cutting out when in lower revs and is running ruff sometimes at higher revs, anyone got one for sale what they know works, mine is the blue labled one, its driving me crazy, and for a new one from subaru costs 365 pound....total rip off.

 

1v ish iirc not sure if it varies from model to model though.

 

MY00... ignition on engine cold 1.02v
Engine warm on idle 800rpm 1.28v
Engine warm ignition on 1.04v

This is on a six month old maf, as myblackwrx has said above models varies.

 

That's way off. It's impossible to give you an exact expected figure because the amount of airflow varies slightly with engine speed, coolant temp and so-on. However, when warmed up you should be seeing something in the region of 1.24-1.36 volts at normal idle. That's the ballpark, so 3.1 odd is way out. With that sort of voltage your ECU will think the engine is ingesting a couple of hundred grams of air per second - although, closed loop, the lambda sensor will be pulling the fuelling back.

What it's doing under boost is anybody's guess but that MAF certainly can't be trusted.

While new ones are expensive from a dealer, they have one quality you won't get with a used one off eBay: You can be confident it'll work properly.