Toyota Repair: 94 toyota Landcruiser, air fuel mixture, nox levels

Question
I recently went to get an emmissions test on my 94 Land cruiser and my vehicle failed due to high NOx levels. The employee there mentioned that the cring everytime a vehicle like mine comes in. He said they have one of the highest failure rates. My question is why is this vehicle prone to these problems and what can I do to get these readings down.

Thank you
Dane

Answer
Hi there,

There are several reasons why a car will fail an emissions test. Please see my list below, I will list some for you:

Misfire condition
Malfunctioning or improperly adjusted EGR valve
Failed oxygen sensor
Leak in exhaust tubing upstream of converter
Excessive carbon deposits in combustion chamber
Improper spark advance
Overly lean air-fuel mixture
Damaged cold air duct
Failed or malfunctioning catalytic converter