So my dad bought this S90, and he writes on here as Gundyj (see next post down). The shifter is fixed, now better with a piece of rubber tubing. Anyways, the issue at hand is related to a cylinder 6 misfire at idle. The idle is rough on the car, because cylinder 6 doesn't really ignite at idle. We have done the following:

1) checked for spark--definitely spark
2) switched coil pack just to be sure--no change
3) switched fuel injector with another--no change
4) cleaned throttle body(shouldn't make a difference but it was dirty)
5) Cleaned IAC valve--no change
6) Checked for air leaks around intake to #6--none detected
7) Checked spark plug--after only 100 miles on the new plug, it was black as anything. Probably partly due to idling for 20 minutes while we're snooping around and that cylinder isn't firing. Cylinder 5 plug is nice and clear. Also, I looked down into the combustion chamber of 5 and 6, and 6 definitely looked like a dirty throttle body, so there's oil and such in there.

The car runs fine off idle. No hesitation and smooth all the way up the RPM range. Could a valve seal have gone bad and be leaking so much oil in that the cylinder would misfire? Could the headgasket do the same? There is also a fault code saying that the air intake temperature sensor isn't working....I must admit my knowledge of Volvos is mostly on 240's and 740's so I don't know what that part is. Any help would be great, as we're moderately stumped....and we don't want to tear the whole head off or something like that without being sure we know what's wrong. thanks as always,

Nate Gundy
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'86 240DL sedan, 260K miles, M46, K cam, 25/21mm sways, 260 front and wagon rear springs; http://valvespringcompressor.weblogs.us/