Low fast idle on cold start causing charging problem

[Normand]

Hi to all,

When cold starting my wife's Wave 2005, 1.6L, automatic, Ecotech II, 46000km (29000mi), the battery light stays on in dash panel. After a little kick on gas pedal (more than 1600 RPM), light goes off. Restarting the engine and battery light doesn't stay on... Was like this every days.

I began changing my serpentine belt because so many cracks were on it and I suspected alternator was not running at normal speed. Was OK for 10 days and then problem came back.

Then, I noticed on the first start when cold, motor never revs higher than 1400-1500 RPM before falling to idle speed half-a-second later at 1100 RPM. I put a voltmeter on the battery and noted 12.4V. After very light kick on gas pedal... 14.6V. So, alternator malfunction...???

I disconnected the alternator cable from the battery post and tested it thoroughly. I put the meter on the alternator connexion and I can reproduce the problem. After starting, when the alternator is not connected: 1.9V. Then I connect the alternator on the battery: 12.4V. After going higher than 1600 RPM : 14.6V. Always like that, cold or hot start... I think it's the normal functionning with the electronic regulator inside the alternator. It needs a revolution higher than 1600 (a certain amount in alternator revs) to switch the regulator.

I conclude the problem is with the level of the fast idle at cold start...1450 RPM... After the first start, fast idle always reach about 1700 to 1900 RPM and the charging circuit is OK.*

What's the normal fast idle speed at cold start?
How could I put it back to normal?
Have you seen a problem like this before?

Thanks,
Normand
French Canadian

[wuwei37405]

That's a lot of information. Can you summarize your problem in one short sentence?

[Normand]

That's a lot of information. Can you summarize your problem in one short sentence?

Peak of fast idle at cold start is too low (~1450 RPM), giving problem with alternator's regulator circuit not switching ON and battery light panel stays ON after start. Brief depress of gas pedal to bring RPM's higher than 1600 switches regulator ON and battery light shuts OFF...

Normand

[wuwei37405]

Thanks. I understand the problem. It may take you a while to find a solution, but the first place that I would look is at the battery. Make sure that the battery cables connections are clean and tight.

[Normand]

Thanks. I understand the problem. It may take you a while to find a solution, but the first place that I would look is at the battery. Make sure that the battery cables connections are clean and tight.

All cables connections are clean and the charging system is working perfectly after I increase RPMs to engage electronic regulator in alternator...
The problem is: low RPMs at cold start (peak at 1450 then 1100) ...causing regulator to stay OFF untill I increase RPMs over 1600 for fraction of second.
Kind of air/gas mixture adjustment or injectors opening time problem at cold start... but don't know where to begin with that.

Normand

[wuwei37405]

I coud be wrong but it sounds like you have a problem with your charging system and not your idle speed. Check the alternator belt to make sure that it is tight enough. After that, you will need a meter and/or a technician to check the various components of your charging system.

[petrified.rabbit]

I say replace your coolant temp switch? only because it is not setting high idle like you want.

honestly though, i dont think my car peaks at 1450 on cold start. i do get about 1100 high idle for a short short time, and then it drops down to about 900. I have an 09 though. How quickly do you expect the alternator the charge the battery. many alternators dont give more the 13v at idle... if you start driving sooner an not idle the car to warm up the issue would go away.

also if you replaced the belt, great, but if you didnt do the tensioner, would you expect it to tighted the alternator contact for slippage?

[Normand]

Rabbit,

when the belt was changed, the problem didn't came back for ~ 10 days. At this time, I did suspect some slippage from alternator or tensionner, but my mechanic said he checked these parts when he changed the belt and they were OK.

Now, with your hints of 1450 RPM at start is normal, I will try to investigate the feet/min from main pulley, belt and alternator to find out any slippage caused from bad tensionner, seised bearing, etc...

By the way, if I press gas pedal after start, everything works perfectly with charging system: 14.6 volts at battery and if I put a load (head lamps), the alternator drops only at 14.4 volts. So, I said to my wife to kick the pedal if she leaves the car running for a while after starting it (it was cold here few weeks ago...)

Thanks,
Normand

[petrified.rabbit]

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?

[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