Idle Reset Tips

Thanks to Leigh Smith on the V6SHO Yahoo! Group for these tips:

I chased a random idling & stalling problem on my stock 94MTX for 9 months. Carefully going through the idle re-learn procedure fixed most of it, for a while. But mine gradually returned and kept getting worse. I also learned a few "tricks" along the way that I feel like sharing. I hope they help you or someone:

I replaced almost every sensor, plug, wires, ISC, coil, etc under the hood, all to no avail. Finally I changed the DIS module, more out of desperation than anything, and the fact that it was the only thing left that had not been changed, and that cured the random stalling problem instantly.

Learned Trick #1

Understand there were no codes or clues pointing to my slowly failing DIS, almost all clues said it was the coil, but I tried 3 of those.

After the DIS module swap I realized that my idle behavior had not been exactly correct for years.

So for you I would try the idle re-learn procedure first.

Learned Trick #2

The AC compressor gave me big trouble because it would cycle on/off quickly, before the engine could "learn", because it was too cold out. So it was almost impossible to re-learn the idle properly. I had to bypass the cycle switch because of the weather, and let it run for 30 seconds straight compressor "on", then "off", manually switching, to relearn idle with respect to AC. If I didn't do that, it just learned "badly" and got more and more confused, cycling from 1500 to 300 in my driveway. (It had me thinking it was possessed.) In warmer weather this should not be as big of an issue, it just depends on how long the compressor stays "on".

Learned Trick #3

Seconds after the idle relearn, compare your idle speed to mine with a perfectly functioning DIS. Mine would not idle perfectly until I got a new DIS. For those of you who forgot, and I did, even after 17 years of driving these cars, a SHO idle should do all of these things listed below, and any degradation here may mean the DIS is slowly failing: (These are listed in the Probst book somewhere.)

• Idle rock steady at 800.
• AC compressor cycle "on" is immediately compensated, with no idle drop, and idle actually increases to 900.
• PS and brake lights no effect on idle speed.
• On decelration while moving, idle falls to around 1200 as long as car is still moving. Doesn't drop to 800 until complete stop.
• Hardest situation, pushing in clutch while slowing down, applying brake and turning wheel, AC cycling, idle should not falter/stunle/stall, should be 1200. Mine could not do this for a year or more. Mine stalled immediately and frequently if the ac kicked on mid turn.
• Cold idle speed goes to roughly 2200 depending on ambient temp. Drops quickly in several 200-300 steps until normal 800 idle after a minute or two. Several disctinct drops is the key. 2200/1800/1500/1200/900/800 or something like that.

Learned Trick #4

Also low rpm behavior is greatly improved (from say 800 to 1800). The lean soft throttle condition at part throttle is gone, engine feels much more torquey in that range. So much so that I can easily drive it all day in traffic, shifting at 2300, and still keep up with traffic. Torque there feels like it is up 25% or more. I could not even drive it in that rpm range before with the bad DIS. Now I can, I shift at 2300, the revs drop to 1500, it drives just fine, and my gas mileage shot up 2.5 mpg to 21.5 driving this way vs running it to 3000-3500 all the time. I'm not saying I drive it this way all the time, it was just a test. But the engine feels much more torquey and it is more flexible than before. Kind of hard to quantify other than that. The point is it was almost impossible to drive it like that with the slowly failing DIS.

Learned Trick #5

If your normal idle speed fails any of those tests, I would do the idle re-learn again, or try to find someone with a known good DIS that you could borrow for a quick comparison, good vs bad. You could just throw on a new DIS, but I always like to confirm the part being replaced is actually bad first, and the new ones are pricey, like $200, kinda steep if it is just a "guess".