Mazda 626 stalls in neutral or park

Check the air intake hose for cracks. These can be very hard to see (best to remove and inspect) and can cause this problem. If it's bad you can either replace it or cheap out like I did and wrap a lot of electrical tape around it.

Larry

BB wrote:

Hmmm... '99 is newer than I've got a reference for. I "specialize" in the '79-'82 626s, since I've got an '82 (actually, about two and about a half '82s, if you count parts) and all of those years are interchangable.

Do try wrapping (or if you're into spending money, replacing) the ductwork, though. As others have said, the MAF sensor is likely being bypassed by a leak (even if there isn't one you can *SEE*...) in the ducting, and it's a cheap and fairly long-lasting fix. If it is leaking, that ends up giving the computer falsely low data about how much air is actually being sucked in, which in turn dumps faulty data into the stream controlling the fuel injection, which looks at it and says "Oh... not sucking as much air. Give it less fuel", making the mix leaner and leaner after each sample of engine conditions, until finally it hits the point where it can't stay running and dies.

On the '79-'82, when the A/C switch is turned on, not only is the A/C compressor clutch engaged, but a relay tied into a vacuum solenoid (which is in turn connected to a diaphragm that pulls the throttle lever varying amounts depending on amount of vacuum, sorta like cruise control) kicks on at the same time to boost engine revs slightly. If the '99 has a similar system connected to the A/C, that's probably plenty to override the idle routine and keep it running.