Failed smog check for high nitrogen levels. OBD is giving us a mass airflow signal code...but the car is also missing the preheat hose for some reason. Any chance the missing hose could be responsible for the bad emissions? I don't want to replace the mass air meter unless I absolutely have to.

 

no, that wouldn't do it. a lot of people just take the preheat hose off because of the chance that the airbox thermostat could fail and continually bring in hot air until the air mass meter gets damaged (which happened to my original one)

 

Can anyone suggest methods of determining whether or not the mass air meter is at fault? What are other possible causes of 1-2-1 mass airflow signal code for this vehicle?

 

You might want to remove that and check to make sure that the filaments are clean. Be careful not to damage them during inspection. Also, make sure that the MAS has a real tight fit at the front and rear connections. Any leakage will cause problems.

 

There is no good way of testing the MAFS with home tools. Best to replace with a "known good one", see what happens.

 

as lev says, the only good way to test these is to swap with a good one. if you can find another compatible car, swap with it... since you said 'engine codes', you have LH 2.4, so most any 240/740/940 1989+ (or turbo 1990+) has the same MAF[*]. Earlier LH2.2 cars use a different MAF with a different connector, this won't work.


[*] EXCEPTIONS to every rule. SOME fairly rare late 240's are LH 3.1 and use a different MAF. Some 740/940's are Regina/Rex and don't have an MAF at all.

 

p.s. high NoX can be caused by exhaust leaks between the header and the O2 sensor. the downpipe can get cracks behind it where you can't see them.