Hi all, hopefully you can help. I took my 1990 Volvo 740 GL (Regina) with 196,000 miles to have Georgia Smog inspection, everything passed except the 15 mile NOx levels. thinking ok, I got this, it's just failed slightly and my idle recently started to hunt, so Vacuum Leak! And I did find a vaccum leak, which corrected the idle problem. I also read about throttle body cleaning for NOx, so I did that, and replaced spark plugs and air filter to boot. Car idles like a champ. Took it back in, faile NOx this time at both 25 and 15 mile and hour test with NOx levels worse! Why? What is going on here? Any suggestions anyone?

Things I've done so far. New Cat replaced 20000 miles ago, replaced timing belt 10,000 miles ago, replaced Fuel Pump 20,000 miles ago, FI relay, RPM sensor replaced 50,0000 miles ago. I don't have testing tools and have read other threads indicating it could be fuel pressure, vaccum leaks, have checked for thos, don't think it's fuel pressure with a relatively new pump. Any other ideas? Where is the EGR located on this car?