Hello Everybody.
I have a '93 Nissan SE. About a year and a half ago, I had some major engine work done on my car. Since that time the check engine light has been on. I took it back to the mechanic and he reset the sensors so the light would go off. After a short time at highway speed the light came back on. Since then, I accepted the light and continued to drive. Now I need to have my car smog inspected (California) and the state won't allow the mechanics to certify the emssions of the car with this light on. A pretest showed that the CO and HC were acceptable but the NO was too high. Recently, I had a new oxygen sensor installed but that did not solve the problem. Another symptom is that during the summer when it is very hot and I turn the air conditioner on, the engine stalls at idle. Can someone advise me on what the problems are and how I should instruct the mechanic to repair the car. Thanks alot.
John W.

 

Well since it's been a year & 1/2 & no one can figure out what's wrong why don't you just have your check engine light disconnected...then reconnect after your smog...then worry about the other problem afterwards...I know Cali smogs suck....fortunately I haven't had any problems so far...as far as why it dies with the A/C on I have no idea...does it drop your idle to low? I know my car idles better with the a/c or defrost on because it idles at 900 compared to 700 rpm.

 

The first thing to do is to see what error code is being reported by the ECU. (You can do a search in this site to find out how to do this.) This should give you some idea of where to start. High NO is generally cased by high combustion temp. Perhaps your catalytic converter is going bad. There is an idle up circuit (AAC - Aux Air Control) that is supposed to raise the idle when the AC is turned on. Either the AAC valve and/or the throttle body needs to be cleaned.