Air mass sensor failure in Volvo V70

[rollingon]

Referring to my 1998 V70 XC AWD Turbo 2.4 Auto, yesterday morning it started as normal (one turn of the engine) and ran fine. By afternoon, it was idling rough and needed several spins of the motor to run. Driving over +/- 1200-1500 rpm it felt much as normal, but was rough on idle at junctions. Having a closer look, at home, there was a slight smell of unburned gas, a bit like when an engine floods.

My immediate response was to buy a new lead set, distributor cap and rotor arm, thinking that they were about due for a change anyway and having recently replaced and gapped the plugs. It started a bit more easily after this, and was OK at 1500 rpm but was still idling rough.

I think my problem is with the air mass sensor, or mass air sensor/meter, as some refer to it. I replaced this around two years ago, and expected it to last longer, but does it seem likely that this is where the issue is? Would it be this sudden? My air filter needs to be changed, and there was some dust in the air filter housing, on the intake side, so maybe with the filter getting clogged and not working optimally, some dust found its way to/through the air mass sensor.

With the car running, if I disconnect the air mass sensor, there is a momentary stutter from the engine and then it keeps running (still idling rough though); if I then reconnect the sensor, it kills the engine. Should it do this, or is this a sign of a fault?

The best price I can find for an air mass sensor is $141 from FCP Euro - does anyone know somewhere that can beat that?

Thank you for any input.

[taupehat]

Years ago I had a 242 that had problems with shorts in the main engine wiring harness - that thing is a giant octopus that at the time went for $800 and was thus left alone. One of the problems that harness caused was burning up what an old boss of mine still insists on calling "airflow meters."

There are a number of tests you can do, probably the easiest is to unplug the MAF and see if behavior changes. That'll put it in "limp home" mode, and if the MAF is the problem you should see some improvement, at least with rough idle. If you see a marked improvement, then I guess you're shopping for yet another MAF.

[edit: I just saw where you tried disconnecting the MAF. You may be in better shape after all, but search this site for other more detailed tests you can do for this sensor]

Vacuum leaks are also known causes of rough idle and I can state from what I'm going through right now that gunked-up PCV system will also cause drama. The way you describe things all of a sudden going awry suggests these aren't your problem though.

TL;DR: Test the MAF, and if it's bad check for shorts in engine wiring. Otherwise, look for vacuum or PCV problems.