'95 pickup failing emissions test

[jja141]

Hello, I've got a '95 Toyota pickup DLX 4X4 with the 22RE engine that just failed the state emissions test because the NOx levels were high.

My limited knowledge of engines leads me to suspect that the cause could be either a bad oxygen sensor, faulty EGR system, or a clogged catalytic converter. Has anyone ever had this problem? The only thing I've noticed that may be related is that when I restart the engine after it's already at operating temperature, the idle is low and rough. But after I drive for a few minutes, the standing idle seems fine. It always idles fine when cold.

I also noticed that after the emissions test the computer screen read "vehicle underpowered." Not sure if that is related. Does anyone have any insight or a gut feeling as to why the NOx levels are high? Thank you in advance for any feedback.

[mustang67408]

Originally Posted by jja141

Hello, I've got a '95 Toyota pickup DLX 4X4 with the 22RE engine that just failed the state emissions test because the NOx levels were high.

My limited knowledge of engines leads me to suspect that the cause could be either a bad oxygen sensor, faulty EGR system, or a clogged catalytic converter. Has anyone ever had this problem? The only thing I've noticed that may be related is that when I restart the engine after it's already at operating temperature, the idle is low and rough. But after I drive for a few minutes, the standing idle seems fine. It always idles fine when cold.

I also noticed that after the emissions test the computer screen read "vehicle underpowered." Not sure if that is related. Does anyone have any insight or a gut feeling as to why the NOx levels are high? Thank you in advance for any feedback.

I think you answered your own question.
An underpowered vehicle with hogh NOX,
First make sure EGR system is oprerating properly.High combustion temps can cause this.
The next thing would probably be replacement of the CAT Converter. If the converter has deteriorated and is partially plugged, this will definatly cause excessive NOX if its not reburning the exh in the RHoDIUM part of the cat.
Just a few thoughts