Hi, all. I posted a while back with questions about what a high level of NOx gasses in the exhaust means. I got many very good ideas, most of which suggested I had vacuum leak leaning out the mixture and heating up the combustion. Well, I inspected the vacuum hoses I could find and they all look like new (thanks to the previous owner who took very good care of this car). I am not familiar with all the locations of vacuum hoses, but I did my best. In general, all the hoses (air and liquid) look like they have been replaced. I am very happy about that. This doesn't mean I don't have a bad house somewhere, just that I could not find one.

What I did find, though, was that spark plugs, though in good shape and stock Volvo units, had the gap approximately twice as big as the spec, which is 0.028-0.032 inches. I could not read the nomenclature off the plugs (a bit of corrosion on the outside), so I am not sure they were the right part number. I did measure the gap with filler gauges and it was about 0.070! I quickly ran out to the local auto parts store and bought some Bosch Platinums that were cross-referenced to this car. I took a gauge to the new plugs and it was smack 0.028 with a bit of sliding room for the gauge. So, my question is this. Can a drastically bigger spark plug gap cause hotter combustion? I have not gone for re-inspection, wanted to get some more wisdom first. I am planning to check the intake manifold bolts also to make sure I am not sucking air there. Any other ideas are welcome.

Oh, and I looked at the graphs that I got from the treadmill test. The CO looks normal, not too low as I reported before. Looks like it's comfortably within the limits, but not down in the mud.

Thanks to all!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers,