90q Engine Check Light

["Smith, Kirby A" <kirby.a.smith@lmco.com>]

Yesterday my wife's 1988 90q engine check light came on while she was
driving.  She reported some rough engine behavior at idle, but good
operation at speed.  After some driving time, when she returned to town she
heard a couple of "pops" and the light went off.  This morning I checked for
loose connectors, the intake manifold grounds, etc.  Upon starting the car
the check light illuminated immediately.  I then pulled the codes.  The fuel
computer had the temerity to display 1111, which I think is interpreted as
computer lobotomy.  (How then could it make its report?)  The ignition
computer reported 2143? (don't have my notes here) but for whatever it was
the Bentley lists the response as indicating a knock sensor fault.  I was
unable to clear these codes using the procedure listed in the Bentley.

Am I correct in assuming that both of these faults are unlikely to have
occurred at the same time?   What other failures, such as distributor
timing, might lead to these fault codes?  Will a 1 Megohm or 10 Megohm
impedance oscilloscope be suitable for viewing the knock sensor output to
see if there is any?  Anyone know what the waveform should look like?

TIA

                .... Kirby   (Kirby A. Smith)
                              2 x 1988 90q
                          New Hampshire USA