I'm working on my 94 850. When I have the key in the second position, I hear a constant buzzing or humming coming from the idle air control valve. You know the round cylander attached by two large hoses and a wire harness. It's staying on as long as I leave the ignition on. I grabbed an extra one at the salvage yard today. Can someone help elaborate on this? It's function etc. is this a malfunction? Should I replace? Thanks.

 

That's what they do, kinda like having a wife in the car without the radio on. LOL

Start the car and the motor will drown out the sound it makes.

 

It's likely doing it's job just fine but if you're in doubt you could clean the one you picked up and install it. It's an idle air control (valve) motor. Not sure if that's the correct Volvo name for it but that's the generic term for it. It controls the amount of air that bypasses the throttle plate to maintain a proper idle speed for engine requirements. When the AC kicks on or you put the transmission in gear and the idle drops from the added load the computer opens the valve inside to allow more air (added fuel too) so the engine comes back to a steady constant idle. It's constantly opening and closing to maintain that steady idle. It does get gummed up over time and cleaning it out with carb cleaner wouldn't hurt. You need to keep the electrical connector end UP when you spray it. You don't want the cleaner and the loosened crap going into the motor. If you need to scrub a bit use a cotton swab but be careful with that wheel that controls the air flow. Let it dry out thoroughly before you reinstall it.

 

Thanks for the advice, my only concern are those large heavy Guage hoses. The one I removed from the other car; the fuel has dried them out, so if I do mine, I have to plan on them cracking, especially with those press clamps they have. Better have spare hoses just incase. Thanks.

 

Need to replace all of the old rubber under the hood anyway. I usually troll the jy and pull newish stuff like that off of cars I see there. Got a throttle hose a few weeks ago and pulled a coolant bottle yesterday. Always looking for those nice $7 - $11 Volvo elbows. The jy usually give them to me if I buy something else that cost over $15.

 

Ive been putting up with a mysterious rough idle that happens maybe two or three times a week (not a constant). Whenever I have the shop check it out, the hesitation does not occur so there is no diagnosis... I am now leaning towards Throttle Body/ Idle Air Control Valve being gummed up. Ill give it a thorough cleaning and report my outcome. Hopefully fixes this irritating problem.