As some of you may recall, I have recently replaced the head on my 2.6 Trooper with an AMC head. Its all back together, and runs beautifully. But there seem to be a couple problems.

It failed the California smog test today. The NOX was a bit high-- not too much, but enough to fail. Everything else tested within tolerance. The tech suggested that I retard the timing from 12?btdc to 9?btdc, and that that would bring the NOX down enough to pass. Anybody have any experience with this?

What causes high NOX? Might there be some other area which is the problem, and the high NOX is only the symptom?

The other problem is the idle speed. The idle speed wanders. I set the idle speed after I did the timing, and it was perfect. But after driving, when it comes back to idle, it might drop to 1200 RPM and stay there, or it might drop to 400 RPM, and stay there. Simply put, the idle speed wanders when it returns from a higher speed. That is to say, it returns to a different idle speed. If I let it sit at idle, it remains constant, though not necessarily at the speed I want. It does not return to the same idle speed two times in a row. Any ideas?

All help will be appreciated.

Ken