Hello all. I recently got a 91' 940 Turbo, and have been noticing a problem when idling. After I run my car for a while (maybe 15-30 minutes) and get it warmed up, when I get the engine down to an idle at stop lights, it begins to shudder and rattle. The engine RPMs will drop below the 500 mark and drop suddenly then go back up to around 600, but its only while the engine below 1000 while idling that it shakes. You can shift into park or neutral, and get the engine over 1000 or so RPM and it stops rattling. Any help on this would be much appreciated.

Mercury

 

You got a low speed miss. A basic tune up (spark plugs/wires) would be a starting point. The rattling is just due to the vibration caused by the misfire.