2001 Deville with Multiple Misfires

[frank1492]

This Northstar was running flawlessly. On a fairly long
highway trip, it started to misfire. By the end of the
trip I am pretty sure that there were two or more
cylinders misfiring. Please note that I had never
experienced *any* misfires before this event. I
want to make this clear because I think this
diminishes the likelihood that plugs are involved,
although the plugs have not been changed in
some time.
Plugs are very expensive to change in this
car and only the dealer will change them. As
the car has 150K miles on it and has other
non-engine problems, I am trying to avoid
spending money needlessly. If possible, I
would like to examine all the less expensive
possibilities first, ruling out everything but the
plugs before I "bite the bullet." (Around $400.)
Could someone list all the other possibilities
that might be making this engine misfire on
multiple cylinders, and that could cause this
to occur suddenly? Note that the misfires could
be random.
Many thanks for your help!
Frank

[caddydaddy]

How many miles are on the plugs? That would be my first guess! I can't believe no other shop will change the plugs, They aren't that hard!
Other than the plugs, I'd check the fuel filter, to make sure it's getting enough fuel. Also check the computer codes to see if it says anything, other than the obvious misfire codes that are set now.

[frank1492]

Codes are as follows: 300 Multiple Random Misfires, 1359, 1360, Ignition System. So I would guess it's electrical.
With the sudden start of this, why would you guess plugs? We have *random* misfires. Is it likely that in the space of an hour multiple plugs would start firing *randomly* if it was a plug problem?
Many thanks for your help, BTW.

[caddydaddy]

Bad plugs can do what you describe. And I've had a car that ran great, then all of a sudden misfired at high RPM's. A change of the plugs cured that.
But since you do have the computer codes that are leading to a electrical or coil problems, I'd look into that. Do you plan on fixing it yourself, or taking it somewhere?