My '86 505 turbo engine gradually developed a pretty rough idle during the
past couple of months. The RPM-meter is oscillating around 900 RPM with an
amplitude of about 200 RPM and a period of about 1 sec. This is accompanied
by slight engine misses. No power loss during regular driving has been noticed.
I remember renewing the spark plugs in January of '96 (about 12,000 miles
ago). Does anyone know how often should the plugs be renewed on the N9T
engine? Any recommended brands and their respective gaps? The Haynes manual
does not even mention the N9T....
Hopefully, new plugs will cure this problem...