My wifes volvo 940 is stalling at idle every few days. The car idles at just under 1000 rpm, the needle moves up and down just a little, is this normal or should the needle be completely stationary? Occassionaly the rpms drop shaking the car and making it almost stall and then sometimes it drops so much that the car does stall. Also a couple of times shifting from park to reverse has caused it stall and once I made it stall when in park just by applying the brakes. I restarted the car and the brakes continued to reduce the rpms every time I applied them, the next morning when I started it to go to the mechanic it was fine of course.
I just went to a Volvo mechanic who says it is not the throttle body or fuel pump so he changed the radio suppression relay but I am still seeing the rpms dropping intermitantly at idle and intermitantly drop after shifting into reverse.
I would appreciate any advice on this matter, thanks.

The RPM needle should be as steady as a rock.

This is the fun part of owning an old Volvo. Let me at it! At this point it could be anything. Good tip, the idle is changing when you apply the brakes. What I would do is check all the vacuum hoses first, STARTING with the brake booster vacuum hose and check valve. Include the vacuum hoses at the charcoal canister including the canister fitting that is plugged. Sorry, IIRC, you will have to remove the canister to get to the hose ends. From there what is the condition of the tune up parts? Plugs, wires, cap and rotor? Check the OBD codes, not that you can trust them. If you have not done this before, don't worry, you cannot break anything. Instruction are in the FAQ.


http://brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm

thank you I will try your suggestions

If the throttle body throat and edge of the throttle plate have been properly cleaned then my money's on a dirty/sticky/worn idle air control valve. This is a very common problem and consistent with your symptoms. From idle, pressing the brakes, running the A/C and shifting into gear all require the IAC to be repositioned to maintain idle. Initial cold idle also requires opening the IAC. Movement of the IAC should be smooth, but if it is dirty or the commutator has contact wear grooves then movement may be hesitant and rough idling or stalling often occurs. If you can force or catch too low an idle or a rough idle then rapidly tap the side of the IAC with the end of a stick. If the revs change, particularly if they return to normal, then the IAC is sticking.

If it's just dirty, you can attempt to clean it; in fact this is part of routine maintenance. Remove the IAC for a through bench cleaning. Rinse the valve area with carb cleaner or solvent keeping the motor section up. Shake the solution around to work it in. Flick (as in rapidly twist) the unit back and forth vertically to work the valve shaft, then drain the excess. Repeat one or two times more until it rinses clear. If you try to rotate the valve manually to open it, do so without marring the metal and note that the normal rest position has the valve slightly open *beyond* the fully closed position (i.e. to open, go the opposite way). With the motor end down, work some WD-40, penetrating oil or a thin lubricant under the valve piston to flow it down around the shaft bushing. Hold it vertically with the motor end down and flick it some more so the valve shaft rotates to work it in. Rinse briefly (still with the motor end down) to remove the excess oil, dry and re-install. There should be additional info in the 700/900 FAQ.

You have an LH 2.4 system. At the OBD-I test socket, run diagnostic test mode 3 in socket 2 to fully exercise engine components including the IAC -see this section in the 700/900 FAQ for details. This can help work in the lubricant and smooth out any contact wear grooves in the commutator. You'll hear the IAC clunk as it slams fully open and springs back closed (you can put your hand on the IAC to feel this). Let the entire diagnostic cycle several times (like maybe 6 times). If the occasional stalling continues and all potential vacuum leak sources have been thorughly checked as suggested by the other poster then you may have a worn IAC and replacement will be necessary.

Hope that helps you.
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Dave -940's, prev 740/240/140/120 Never overestimate what little I know.