"Special" spark plugs--what do they do??

Right, and there's no reason to leave plugs in for 300,000 miles.

How about 200,000 (there was one original plug in my Supra. Actually didn't look *TOO* bad, the electrode was there but the gap was .090...)

It makes no sense for the side (ground) electrodes to last such a long time since the center electrode will not last that long. In a well-designed spark plug, the center and side electrodes will have roughly the same life.

"Ernie Sty" wrote in news:NfmdndtTI8Eo7BDbnZ2dnUVZ snipped-for-privacy@giganews.com:

Interesting thread but I think the answer is rather obvious. When something unexpected happens we immediately credit it to whatever we know was happening at that time, and when we find the cause it is not related in many cases. In this case, the cause of the increase in RPM was not pursued and someone decided it was because the spark plugs were changed. Odds of that being the case are pretty much zero.

Well, maybe in that car, but in my Supra changing the plugs caused a big jump in idle speed.

This is because the computer was compensating for the lousy plugs in the car, and when correctly firing plugs were installed, it threw the idle way off. Pulling the fuse to the ECU reset the idle properly.

I believe within the limits of the ISC valve your Supra should idle at the proper RPM even out of tune. Removing a spark plug wire just makes mine idle ruff at the same RPM anyway. Maybe the valve is gummed up.

Dan

Oh ya, I always thought the reason real good spark plugs have a smaller diameter electrode's is so the spark will be more powerful or what ever than a wider electrodes wider/weaker spark is.

Maybe more intense or precise or hotter would be better words. IDK...

After checking the timing, the car was idling at about 1100 RPM! Removing the fuse for 30 seconds reset the idle to 700, right about where it should be.

Well then, you must have superior intelligence! Hats off to you, hurrah!

Exactly who is included in that "we"?

The cause of the increase in RPM *was* replacing the spark plugs, because that was the only thing that changed.

I can see how one might think that unless they knew something about car engines and spark plugs. If the old plugs were worn out, gunked up, poorly gapped or the wrong type, they could have been causing the idle speed to be abnormally low. Simply putting in fresh plugs would then increase the idle speed.

That makes sense, if it has an RPM sensor that feeds into the idle speed regulator connected to a throttle/FI. The other car, the SkyHawk, was older (probably mid-1970s) and probably had a throttle positioning screw or whatever they had then.