Bad Idle...

I have a 98 (also bought used). I also used to have a 99. Both idle(d) a little rough. Spring and Fall are the worst. I think it is becasue that's when the gas makers are switching over their formulas for changing temps.

How much is a little? Mine bounces anywhere from 700-1200 rpms everyonce in awhile. In general though, it's not noticable on the tach and it idles just bumpy enough to keep the kidney stones movin !

The tach stays constant. You can just feel it in the steering wheel and everything else. If you look at the motor too you can see it kinda missing here and there.

If you have'nt already, pull your spark plugs. Check the spark gaps, look for electrode wear, and deposits.
Replace them with OE plugs if there's any question.
If you still have a rough idle afterwards, at least you know the usual cause is eliminated.

I have found that the usual cause for a rough idle in my rigs is a vacuum leak.

Quick test - get a can of spray carburettor cleaner. Let the engine get DEAD COLD (overnight sitting will serve.)

Grab your carburettor cleaner, and start the engine. While the engine idles, spray a fog of cleaner (don't use the "straw" - save that for when you need it later) all around your vacuum lines - especially any junctions you see. Don't forget to fog the mating surface between the intake and cylinder head.

When the fog gets draws in and the idle races, you've found the leak.

I've also found it a good habit to just check torque on the manifold bolts about once a year - I usually find one or two have worked loose, and the slightly funky idle I've developed in the meantime will go away.

5-90