Uber low idle when warmed up.

[Whisper]

A while ago I started having issues with charge light coming on when running cooling fans and/or A/C. I thought it was the alternator, but now I think I figured it out - my idle is too low. When fully warmed up (maybe 5 - 10 minutes of driving), my idle is at around 400 or so, and if the engine is running a bit warmer, it's even lower. Car doesn't stall, in fact it idles smoothly (which is probably why I haven't noticed that it's so low), but if I turn on cooling fans or run A/C, my charge light comes on after a few minutes. I guess the alternator is not spinning fast enough to compensate, so it starts to drain the battery. If I gently hold down the throttle to bring the idle speed to above 700, charge light goes off.

Since this is a relatively recent development, as the car used to idle at around 600-700 last year, and I haven't played around with idle adjustments to cause anything of the sort, I suppose something is going bad. First thing I thought about was the IAC, however I'm not sure what resistance it's supposed to have when warmed up... FSM says 10-12 ohms at 20C, but does the resistance go up or down when it's hot? I just measured about 13.5 after driving and then letting the car sit for 10-15 minutes or so. Is that within spec?

[RX8SE3P]

Have you shorted out TEN and GND in the diagnostics box and then turned the idle up a bit? Or wont that work?

[Whisper]

I don't know if that will work. Idle is ECU controlled, so even if I adjust it, ECU will try to bring it back to where it thinks it needs to be based on the inputs. Plus if my IAC (or something else) is bad, then adjusting is just a band-aid and not a real fix.

I'll try to play around with it, but I don't know if that'll be any good.

[RX8SE3P]

Thus the whole reason people say you must put it into diagnostics mode.

When you put it in diag mode, it disables the computer from making changes.

So you can then adjust timing and idle etc. If you don't put a jumper wire between TEN and GND then the ECU will correct any settings.

I think you should try it before going and changing expensive parts.... all you need is a paper clip and a screw driver lol. Can't get much easier than that.

- Jumper wire in TEN and GND

- Turn car on

- Adjust idle to where you want

- Turn car off

- Take out jumper wire

- Turn car back on again and see if it idles better

[mx3boyze]

I had a problem with my ZE when I first swapped it, Jumping TEN and GND wouldnt do anything once I shut it off and remove the jumper it would go back to where it was before I had adjusted it. Ended up being the throttle stop screw.

[Whisper]

I see. I'll check it out.