Canadian Nissan Truck Club

IDLE EMISSIONS
A vehicle that has sharply elevated HC or CO emissions at idle will usually have a noticeable misfire and/or rough idle. The most likely causes here would be:
Fouled spark plug(s);

Shorted spark plug wire(s) or defective plug boot(s);

Vacuum leak;

EGR valve stuck open;

Burned exhaust valve;

Misadjusted throttle body air/fuel mixture; or

Misadjusted carburetor idle mixture.

An extremely rich fuel condition can also cause elevated HC and CO at idle, while an extremely lean condition will only cause HC to rise abnormally. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle.

HC and CO will be somewhat higher as a cold engine warms up because the fuel system may still be running in open loop. Until the engine reaches a predetermined temperature and/or the oxygen sensor gets hot enough to produce a good signal, the PCM will supply a relatively rich mixture while the system is in open loop. A faulty thermostat that is stuck open or a defective coolant sensor may prevent the system from going into closed loop.

NOX emissions are always lowest during idle and decel because that is when engine load and combustion temperatures are lowest.

Fouled spark plug(s);

Shorted spark plug wire(s) or defective plug boot(s);

Vacuum leak;

EGR valve stuck open;

Ozzker wrote:plugs and wires SHOULD be new, according to the PO. they look pretty nice too, so I think they are. Vacuum leaks may be the case, I will have to search, and I haven't even looked at the EGR yet, it may be faulty, who knows. Its running very nicely, no miss, no rough idle, nothing. It idles at 750-800RPM no problem.

Now, I know the Rad is **I have a filthy mouth, pass the soap**, and it did overheat while idling once today. For the test, i had them stick a massive fan into the grill to keep her cool, and she still got warmer then she should. Would changing the Rad make a difference, I have a newish one sitting here that I haven't gotten around to installing yet!!

studum wrote:

Ozzker wrote:plugs and wires SHOULD be new, according to the PO. they look pretty nice too, so I think they are. Vacuum leaks may be the case, I will have to search, and I haven't even looked at the EGR yet, it may be faulty, who knows. Its running very nicely, no miss, no rough idle, nothing. It idles at 750-800RPM no problem.

Now, I know the Rad is **I have a filthy mouth, pass the soap**, and it did overheat while idling once today. For the test, i had them stick a massive fan into the grill to keep her cool, and she still got warmer then she should. Would changing the Rad make a difference, I have a newish one sitting here that I haven't gotten around to installing yet!!

Open up the Distributor and take a look. When I was chasing my misfire I dismissed the cap and rotor because they were supposed to be new also. Even looked pretty as you say...

When it was opened up a socket was found inside and the tip of the rotor was bent up at a 45 degree angle. Wasn't the end of my misfire, but still...

Good luck

adamzan wrote:The TBI pathys have some funky emissions poop near where the newer wd21 airbox would be. Have you checked that none of it has been disconnected?