The car's running smoothly, according to my wife; check engine light came on today, with the trouble codes being "random misfiring," and "misfiring, cylinders 3 and 4" (separate codes, of course). It's not doing the desperation flashy dance that would signal catalytic converter hazards. The repair shop we use suggests clearing the codes and watching for recurrence.

I replaced the ignition components early this summer for the smog test: distributor rotor and cap, plug wires, plugs. Since then, we've driven it almost daily, around town and occasionally around the county. I haven't popped the cover yet to see if there are visible wire problems.

About 170,000 miles on the original motor, repair shop reported earlier this summer that it was looking/testing as being in good shape, good compression and all.

From the research I've done here (dang, what a resource this place is!), it looks like we should:

Drop in a bottle of Seafoam on general principles.
Move to premium gas from the low-octane we've been using (we get 30 mpg on the freeway even with the cheap stuff; neat little cars, these).

If the problem recurs:
1. Do a general inspection for problems (wires failing, loose, etc.)
2. Pull plugs on 3 & 4 and clean them. Possibly switch plugs to, say, 1 and 2 from 3 & 4 and see if the problem moves.

After that, because my time and tooling are both limited, I'm inclined to take it to our shop for finer diagnosis, unless there's some other simple test I'm missing.

Your thoughts will be appreciated.

I'd start with checking the plugs, not seafoam. If they're oil coated, you might have a leaky gasket on the fill cap that is floating down into 3 and 4. Usually that'd just be 3, but.. Black plugs could indicate stuck injectors (which seafoam would help with..).

I'd pull and check plugs for obvious problems. Then move plugs (don't forget to write down where you moved everything!) to see if problem moves. If I still didn't know whats causing it, I'd pull distributor cap to see if there's any damage on that side. If no clues, time for a compression test.
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If you're not driving it "like its stolen," are you really driving?

How many miles and what kind of spark plugs did you use.

switch to 89 octane immediately, the 87 octane contains no cleaners and burns hotter. If you tank up with 91 octane, that will add cleaners and boost the current octane to at least 89.

Good garage advice, clear the codes. Yes, I would pull the plugs. Clean them with a wire brush and check the gap. If they are the 3 prong variety and very dirty, you are running rich - check the vacuum lines for a leak.

If you have a non-turbo, check the thermostat flap at the air cleaner. All california cars should have a closed flap, it never gets cold enough to warrant warm air.

Klaus
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Did you do your Random Act of Kindness today?