That explains the funny adapter hose deal I have on my '87. 3/8" hose ran up to a brass barb adapter down to the 1/8".

I couldn't imagine any of the moulded vapor/vacuum hoses are in great shape with that many years of age. I recall replacing all of the petrified bits when I was going through my engine.

Do you have any pictures of your procedure?
Is The sensor mounted under the upper intake?

Thanks,

The sensor is on the firewall, but it connects to the upper intake using a hose that's 3/8 on the manifold end and 1/8 at the sensor. The big end is clamped on. You might get lucky with needle-nose pliers, but you're still working under and behind the upper intake. Far easier to take it off. Sometimes you do more work to save aggravation.

I didn't take pics, but picture two short pieces of steel tube, 3/8 and 3/16, butted together, flared, and brazed.

Thank You,
I am not sure this is my issue or not, but worth looking into. I seem to have an inconsistent miss at idle and if your under light load moving 15 to 20 mph you can feel it miss, or jerk a little bit. If you step into it, doesn't miss. If you flat floor it, doesn't miss at all the way up the rpm band.

I have been leaning towards an injector beginning to fail, or the tip is plugged up a little.
I guess it is possible it could have a valve sticking, but I don't really think so.

I'd be looking for vacuum leaks or a sticking EGR valve.

hadn't thought of the EGR valve. I could unplug it and see if that changes anything.

Thanks for the tip.
I found the MAP sensor. Its all original as I was sure it was. Had the car since it had 44K on it. Probably need to check that hose for cracks.

The way you test the EGR is, get the engine up to temp, let it idle. Unplug the IAC, remove vacuum hose from EGR and plug it. Put a Mityvac on the EGR and give it 5-10 inches of vacuum. If the engine stumbles, and recovers when you release vacuum, the EGR is OK. No stumble, valve is stuck closed. Stumbles and doesn't recover, valve is stuck open. Replace either way.

Thank You Sir,

Was the misfire cured?

Not sure. Last time I took the trip, I drove the Mazda. The Valley Of Misfires is about an hour away.

Final update: The misfire was pretty damn persistent. Decided to look at plug wires again. Although no obvious flaws were visible, I added some split-loom on the driver's side where the wires pass by the airbox mount, and re-routed #2 and 4 on the passenger side, so they don't run next to each other. Also separated 7 and 8 a little bit.

This, in combination with setting the timing properly (it was about 5 degrees retarded), seems to have fixed it.

To rule out something else; could be fuel related. I would pull the injectors out and check the spray patterns. You may have one or more injectors shooting an upside down "v" pattern or a fuel stream sideways where the fuel is only wetting the sides of the injector holes in the intake manifold and not shooting fuel into the intake valve. This could cause the issues that you are experiencing.

Could have been, but wasn't. See the reply previous to yours.

Try disconnecting EGR valve and plug vaccume line