Can anyon help solve the mystery? New Cat,plugs, cleaned carbon, timing,so far, all mechanics have been stumped... Volvo next week in desparation.. I have never run into this before as my 87 240 has always passed (has only 230K).

Have you set the Basic Idle Mixture?
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john

will do, thanks John

My son's first Volvo (1987 744T) failed the NOx part of the emissions test on the first try. Setting the Basic Idle Mixture made it pass. The car had about 180,000 miles and original CAT.
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john

With a new cat, the NOx ought to be right on. However, the mixture could be too rich or lean, either from improperly adjusted base mixture or from vacuum leaks. Vacuum leaks are pretty simple- inspect the big black air hose for splits and cracks, and try spraying carb cleaner or similar spray (WD40 works too) around the intake, looking for leaks- idle speed will go up when you hit a leaky spot.
If there are no leaks, I'd suspect mixture, and you can adjust it with the scrwe on top of the AMM (might have a plug in it). Note that the timing must also be right, and if it's advanced, you'll fail on NOx and possibly CO. You can retard the timing to zero, and get emissions WAY down, but it will be down on power badly as well. You could, um, adjust it back afterwards.

Other less likely things: fuel pressure too high- bad fuel pressure regulator
Air filter restricted- need new filter
Bad injector seals on manifold- need new seals
Bad plugs/cap/rotor/coil wire- any misfires will give high emissions.

Good luck!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

Thanks for the great advice, Aye. ... will try all suggestions, and get back with the news.

Did you check the hose past the AMM. It kinda looks like an accordian. They tend to rub on the side and wear through. You have to remove it to see it. Also check for exhaust leaks.

Your scaring me because I failed NOX and plan on replacing cat tomorrow.

Yama, I wish you a successful inspection!It has been a royal pain in the ass.(and the wallet), thanks for the suggestions.