I worry when someone asks about using a torque wrench on spark plugs. Don't ever overtighten spark plugs. On your car, the specification is only 18 +/- 4 Ft-lbs. That's just hand tight. On any vehicle with an aluminum head, don't tighten the spark plugs at all when the engine is hot. They will become nearly impossible to remove.

Have you noticed any differance in the way the car runs? I would look for other things that you may have disturbed in the process such as vacuum hoses. These were really crappy on my '89 760. You may have also damaged the turbo inlet hose when changing the air filter. These are notoriously problematic when they get old. Are all your injectors firing - easy check by listening to them.Check the fuel pressure regulator also (refer to the FAQ).

If the car is running rough, possibly one cylinder not firing properly. Check by starting with fully cold engine. Start the car and within first few minutes of running, check the temperature of the individual exhaust runners. Just touch them with your hand. If you find one that stays cooler than the other three, you are on your way to a solution.

What brand of plug wires did you use? I have recently heard some horror stories regarding aftermarket wires and ignition components in general. Check to make sure the wires are installed properly. Just to be thorough, note that some aftermarket wires require you to remove the threaded contact at the tip of the plugs to make proper contact.

Good Luck,

Dan