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.

 

Sounds more like a vacuum leak to me; did you ck for one?

Slapping parts onto your car is an expensive way to diagnose something..

 

I didn't notice a vacuum leak, but on finding plug #3 to be fouled, I tested compression and found #3 cylinder to be 20psi, so feel pretty sure the issue is due to the piston ring being worn-out. Now I have a serious decision to make.

 

RockAuto Parts Catalog
They have a few options, this was the cheapest listed.
ULTRAPOWER Part # 0280217107 $$64.89

BUT, before you buy I'd do some more checking like Gdog advised.