Trying to tune idle...

[SQLGUY]

While my bike is rideable, I am still struggling to hit a good combination of cold start, warm start, and, especially, idle parameters.

The main problem I have with idle is that when the bike is warm, if I set the idle air valve to be closed and the mechanical idle to a point where the engine idles OK, it will not return to idle after a rev... instead it will want to stay up at 2.5K to 3K RPM. If I then reduce the idle setting to bring it back down to 1050, it will only stay there for a couple of seconds, then stumble and stall.

Actually, I should say, it was stalling, because the other issue I'm seeing is that when the engine speed drops low enough that it's about to stall, the ECU thinks I'm cranking again, so it opens the IAC back up to cranking position (wide open), which revs the engine up to about 5500 for a couple of seconds. The IAC is a Ford PWM type one. Looking at the code (2.884), this doesn't look like intended behavior. It looks like it should only be using the cranking position of the IAC the first time the engine is cranked after booting the ECU.

Of course, if I could solve the first issue, the second would be much less relevant. Any ideas?

Thanks,
Paul

[Bernard Fife]

Paul,

If the rpm falls below the cranking rpm setting, the IAC will reset to the cranking position, then go to the temperature vbased posituion over the 'taper time'. That's the intended behavior. So you could either:

- lower your cranking rpm setting (it only needs to be 50 to 100 rpm over the actual cranking speed - and should be well below your idle speed),
- raise the cranking postion setting of the IAC to be more near it's final value (this doesn't usually affect starting performance, since the IAC is reset as soon as the engine exceeds the cranking speed setting).

For the warm-up, etc., tuning, that just takes time and/or experience (the more you have of one, the less you need the other!)

Lance.