2004 Mazda MPV Stalling and Rough Idle: Replacing the Idle Air Control (IAC) Valve

I have owned a 2004 Mazda MPV LX since early 2006, and it has been a great vehicle so far. Plenty of room, fairly fuel-efficient, quite practical and very satisfactory on the whole… with one exception.

Starting around late 2007, the minivan started to occasionally stall while decelerating or braking. The RPMs would drop to near-zero and the engine would die. It only happened a couple of times over a few months but began to get more and more frequent as time passed. Generally it would only happen between 15 and 50 MPH, and only when letting off of the accelerator. After the first few times, I learned to avoid it by tapping the gas as I saw the RPMs plummet; if I did that in time, I was able to keep it from dying. If I didn’t however, my only recourse was to shift into Neutral, start the engine while rolling, shift back into Drive and keep going. Of course, this was quite unsafe, and by the time it was stalling once or twice every time I drove it, it was time to do something about it.

I did a bit of research online and found the occasional mention of a faulty IAC valve being the cause of stalling and rough idling. The folks at Kragen didn’t know what an IAC valve was, and I didn’t pursue it any further from there.

The van began to show a check engine light, so I took it in to the local Mazda dealership to have them check it out. It turns out the check engine light was the result of a sensor that was blocked by excessive carbon buildup in the intake manifold, which was caused in part by the stalling behavior. According to the tech, the stalling was causing the engine to run a richer fuel/air mix on restart (because it interpreted the stall as an indication of a fuel/air mixture that was too lean), and this frequently-richer burn was causing an undue amount of carbon buildup. They cleaned out the intake manifold with Seafoam (or a product like it), did a firmware upgrade, changed the plugs and wires (which I’d asked them to do as a maintenance step while they had it in there), and, $1,100 later, was given a clean bill of health. The MPV passed Oregon’s emissions testing, the stalling was gone and all seemed well.

A couple of months later, the stalling started to act up again, and grew in frequency as it did before. I did a bit more research and all available evidence still pointed at a faulty IAC valve. As it turns out, the folks at Kragen weren’t able to find the part I was referring to because it seems to go by several name/acronym combinations: IAC valve, idle air control valve, idle control valve.

Still not sure that a fix was in sight but willing to try it, I ordered a replacement IAC valve from an online parts retailer for around $65 and put it in. Replacement of the valve was very easy; it is attached to the intake manifold by two bolts, and has a simple wire harness attached to it. Here are two pictures showing its location on the engine. I saved these when I was doing my research and, unfortunately, can’t find the original source, but here they are:

Location of idle air control valve on MPV engine

Closeup of IAC valve

As you can see, the valve is fairly easy to locate. It should be in a similar location for the following years:

• 2002 Mazda MPV
• 2003 Mazda MPV
• 2005 Mazda MPV
• 2006 Mazda MPV

Years 2001 and earlier have the IAC valve attached to the firewall, but it should not be too difficult to find (the part itself looks the same as the one seen here).

Since installing the replacement valve around four months ago, the minivan has been running as good as it did when I bought it. There have been no issues whatsoever with stalling or rough running.

Update: Slightly better image of the IAC valve below.

It's the gizmo with the red circle around it.