How long should spark plugs last?
 

1989 22re 23?,??? miles. I noticed that my fuel milage has dropped ALOT in the last few months. I've gone from about 24mpg down to about 15mpg. The cap, rotor, wires and spark plugs were all done at the same time and upon inspection they all look ok. Do spark plugs just "go bad" after a few thousand miles?

I'm doing some work on it tomorrow and figured while I was in there I'd put in some NGK Iridiums. I'm also fixing an exhaust leak, checking the TPS (if I can find my damn meter), trying to clean the EGR (again) and probably doing a valve asjustment.

I just think something has had to have failed for my milage to fall that much in a couple of months.

You said that you had an exhaust leak, that can have an effect on gas mileage.

First things that come to mind are the simple things.
Tire pressure
02 sensor
dirty air filter

Change your plugs.
Ive tried the Platinum plugs and IMO they are a waste of coin.
Stick to NGK or Nippendenso.
Best plugs for the motor are the Denso W16EXR-U, available from most Autozones, or rockauto.com, or get the Toyota ones from 1sttoyotaparts.com - those are Densos. Gap to .032", a teeny bit over spec.