I was climbing a hill in my 1996 965 the other day and it suddenly began running rough. Felt like it was missing on one or more cylinders, so I figured it must be a bad coil pack or broken spark plug electrode. The check engine light did not turn on.
I pulled the plugs, and all six looked the same. Their color and smell says the engine is running rich. Tested compression on each cylinder, and they are all good (200 to 210 psi). Installed new plugs and engine continues to run very rough.
So it's a misfire that appeared suddenly and I'm unable to ID any particular cylinder as a cause. Check engine light now on, but likely caused by my cranking engine with fuel pump and coil packs disconnected while checking compression.
Any ideas?

Thanks for your advice. I pulled a P0303 (misfire #3) and P0410 (air injection fail) from a code reader this morning. Also found a rotted rubber elbow where the vacuum lines go through the passenger side of firewall.
I only drove a few miles after initial problem started - probably not enough to change coloration of #3 plug. I'll check these out and get back to you.
BTW, when did the decal showing vacuum lines disappear from Volvo engine compartments?

Swap coil pack #3 to another cylinder, clear the codes and drive it and see if the misfire code moves to the new cylinder. If so, replace the coil pack.

Good luck!

Thanks for the advice Herb. Alas, I don't have a code reader so here's what I did. First, disconnected the #3 coil pack and ran engine. Engine ran no worse than before, proving misfire is in #3 cylinder. But is it from no fuel or no spark? So I moved #3 coil pack to #2 cylinder and ran engine. Engine ran worse and I assume both #2 and #3 were now misfiring. Waiting for new coil pack to arrive.
Examining the #3 plug more closely, it looks cleaner than the other five - maybe the unignited fuel was cleaning it?

Installing new coil pack at #3 cylinder solved my problem - engine running very smooth.

Have you checked for vacuum leaks? I’d also check the temp sensor, FPR and AMM. Maybe a code hasn’t been thrown?
--
Will I buy another Volvo??? We'll see....

Are all six spark plugs firing?
Dan