Low fast idle on cold start causing charging problem

[Normand]

sounds like a tension issue to me then, if adding speed fixes a problem>

it seems to only occur on initial start up idle, then the issue does not return?

yes,
only on first COLD startup. At this time, I got 1400RPM for 0.5sec, then 1100 and when the motor is hot few minutes later, 900.*

If I start cold, shut motor off after 2 secondes and then start again, the peak at startup is ~1800 for 0.5sec and the regulator is switched ON and alternator charges the battery even if the motor is cold. All subsequent startups are OK. If the motor is stopped for few hours, the problem is back for the initial startup.

Maybe some bearings are seized (in alternator or tensionner or other pulley) and at the first startup some slippage occurs...but why the idle peak at 1400 on first startup and 1800 at all subsequent ones???

Normand