I have a '91 940 16valve and have replaced the sensor in the air box last year but am now having the same problem of stalling out at idle. My mechanic said too much hot air from the manifold could be frying the mass airflow meter so it wont work correctly. He suggested that we remove the hose from the manifold to the airbox and if the car ran ok it would be either the sensor ($35) or the mass airflow meter ($250). Car runs fine now but I need to get it smogged. Is there any way to clean or rebuild the mass airflow meter or to modify the airbox or flaper valve inside so no air gets thru from the manifold (the car is only driven in California so I rarely woud need the hot air to preheat). Any suggestions would be appreciated.

Stalling at idle, especially cold stalling or when coming to a stop, and where the engine is otherwise operating okay is more commonly a problem with the idle air control system, not the AMM. The next most likely possibility is unmetered intake air from a split in the main air supply tube or one of the vacuum lines.

In my experience, B234F's are particularly susceptible to a dirty PCV system which in turn leads to a dirty throttle body -I'd guess 80% of idle stalling problems are right there. So, the first and most important thing to do is make sure the throttle body is absolutely clean. This is a routine maintenance procedure and for B234F's I would recommend doing it at least once a year or every second oil change. You should also check that the throttle body and throttle linkage are properly adjusted in case someone has been misguidedly trying to correct idle problems by making adjustments -factory settings are pretty much good for life. The primary adjustments are the the idle stop screw and the TPS (throttle position sensor) switch. See the 700/900 FAQ feature section for tips on all this. For more detailed adjustment info you can also refer to one of my earlier postings on the subject. At throttle body cleaning time you should also flush clean the IAC (idle air control) valve, clean/replace the flametrap and clean the PCV system hoses (especially the small vacuum hose off the top of the flame trap). If you continue to have idle stalling problems, especially an idle that seems to stick a bit low or high or that jumps around, then the next suspect is a worn/dirty IAC valve that may need replacing.

The warm-up air by itself should have absolutely no direct affect on your stalling. Disabling this is often done to help prevent the AMM from overheating and failing in the event the air box thermostat fails. Doing this will slightly lengthen engine warm-up and may attract the attention of the smog police unless you hide your work (hint: screw the flap shut in the air box so you can leave the hose connected). In all but cold climates the difference is unnoticeable so many people do this as cheap insurance.
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Dave -not to be confused with a real expert

Thanks for the info. The car has run great since I disconnected the hose from the manifold, (gas mileage has also improved noticably) so I think I'll take your advice and shut the flap permanently since it rarely gets below 40deg. here and I don't mind a little more warm up time when it does. The money I'll save on parts will help pay for my smog check and recently aquired speeding ticket.