I prefer calling them Air Flow Meters (AFMs), because that is what they do. MAF confuses people.
A bit of confusion. There is no AFM that "weighs" air. In this case, the unit has a heated wire running through its air passage. The more air that rushes through the more that wire (s) cools and the degree its cools varies an ohm reading which is sent along to the ECU with a measurement of ambient temperature (so the day's termperature can be discounted from its effect on the wire heat).
Sorta. With the measurement of the wire's heat, the ambient temperature, and the coil pulses the ECU knows the engine load and rpm and, all else being well, it trots to its eprom (fuel map) and finds what it has been told will will keep the local government happy (1st priority) and (hopefully run the engine (2nd priority).
Correct.
It is very hard to misdiagnose them with a LR diagnostic unit. Of course, one can simply connect a multimeter and test the voltage between pin 35 on the ECU plug and a good earth. He should get between .3 -.6 volts. If it is off that, there is something amiss with the AFM.
Not hard to do. One buys a bottle of Quick Start (aka a spray can of ether). When the engine is running, he sprays short spurts of it at various places vacuum leaks may occur, (hoses, junctions, meeting faces, steeper motor, plenum nose, fuel pressure regulator) if the rpms change, he has found his vacuum. It is the only way. Even the most modern diagnostics unit cannot find vacuum leaks.
Actually they're great. These Hitachi AFMs (I am assuming he has a Lucas Hotwire fueling syetem) have proven to be extremely solid. But as you say, if it has gone south, there is nothing he can do about it. So this is all informational and not much use. He should never spend the money on a AFM without it being checked first.
The same symtoms can occur more commonly from other causes. For example, he is far past the lifetime of 1996 lambdas..and a bad one causes all these symptoms.
In his case, it is between the air filter housing and the nose of the plenum. The plenum nose houses/holds the throttle body, the throttle potentiameter and the idle screw. The plenum funnels the air into the trumpets, through the trumpet base and only then into the intake far below.
If I were our friend, I would test the lambdas first and go on from there.
