I have been pulling my hair out to get this car to pass CA smog.

CO is 1.8 and HC is around 280 at idle - FAIL
CO is 0.05 and HC is 15 at 2500 RPM - PASS

1991 N/A 5-speed, 80K miles, all bone stock, California car.

I've spent hours searching here and other sites and following the advice to no avail.

New plugs, new O2 sensors, new AIV filters, cleaned the AIV reed valves, triple checked the timing and vacuum hose routing. New air filters, cleaned the AFM and checked the TPS. Everything checks out. The car runs smoothly and has plenty of power. I rechecked the plugs and they're dry and normal wear. Compression is 180 +/- in all 6 cylinders.

It has to be tested at a "test only" station. So I took it my local mechanic who checked the CAT temps and air injection system. Said all was good.

I took it to the Nissan dealer yesterday so they could run CONSULT and see if anything showed up. The only thing they found was the EGR solenoid valve was not closing all the way at idle so the EGR valve was cracked open a tiny bit.

I replaced the solenoid valve and re-tested. Same results!

I called the Nissan dealer and they're stumped!

Any ideas??

 

Any vacuum leaks, whats the timing set at, have you tried testing the EGR/AIV system with a vacuum pump and gauge? have you check the AAC? Have you pulled the EGR solenoid and tested it? The AIV's and EGR really don't do crap for cali emissions, besides visual and even then most people have no idea what they are looking at. let alone what to look for.

 

AIV was tested and new filters installed.
Timing is at 15
EGR is working
AAC is working
I can't find any vacuum leaks after triple checking the lines.

Even the Nissan dealer is stumped.

 

Update #1
Everything is completely stock including the airbox, all the sensors, etc. It has a new EFI wiring harness too.
Yes, the AIV is working as it should.
I have an ECU out of a 1993 (no AIV) but I might try it anyway.
Yeah, new CATs may be in my future.

The Nissan tech wants another shot at it tomorrow.... We'll see.

Update#2
The ECU does control the AIV, but Nissan deleted the AIV in 1993. The '93 ECU must change the idle mixture to compensate for a lack of extra air in the system. I compared the ECU pin-outs in the FSM. They are identical except that the '93 ECU skips a pin where the AIV was. All the other pins go to the same places.

I found some dirty contacts on the CAS and the AAV. I cleaned them and checked with ohmmeter per FSM. They check out OK.

Tomorrow it's back to test again and if no pass, back to Nissan.....