This is the first time I have failed in 10 years. The failed result is NO (oxides of nitrogen) at 15 mph (1752 rpm). Max allowed is 486 ppm. My measured value is 705 ppm. Interestingly enough, at 25 mph (2050 rpm), there is no problem: max allowed is 502 ppm and my measured value is 145 ppm. Does the different result at these two speeds point to some specific cause? Thanks.

My vehicle is a 1993 940 turbo. I thought it might be the EGR, but there is no EGR listed on its emissions tag so I don't think it has one, probably because it is turbo charged. I removed and cleaned the Idle Air Control Valve (IACV), but it was not very dirty.

If you can tell me how to remove the Mass Air Flow sensor for cleaning, that would help. The MAF is Bosch 272 07 3 A (Volvo part # 0280212016). It has 6 contacts (pin one of which is empty and unused) and 4 very small Phillips screws on top. I'm not sure if I should take out those screws or would it be easier to remove the hose clamps on either end of the sensor to get to the sensor wire?

 

To remove the MAF senosr for cleaning: I removed the 4 tiny Phillips screws on top of the MAF sensor and the sensor did NOT come out, so put them back in. Then I removed both hose clamps on either side of the MAF sensor; then removed the cover of the air box still attached to the sensor; then I was able to spray the MAF sensor cleaner into both ends of the sensor.