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Old 11-15-2013, 09:48 PM   #1
suby6
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voltage and rpm at idle

My lights and dash have always dimmed at idle even with big 3 upgrade. Using the instrument cluster diagnostic mode i can see my voltage seems low at idle around 12.5v give or take. even seen it dip to 11.9. no batt light ever comes on.
Voltage even under load at higher than idle is a solid 14 minimum.

Have also noticed that the rpm seems to sit around 700 at hot idle. What should proper idle for a 03 zetec manual be? Does anyone have a definitive answer? Searching gave numbers all over the place. 700 seems low based on other cars I've owned.

Curious if voltage is lowering the idle or vice versa. No warning lights and doesn't misfire or stumble at idle.

Ive got a tune for 91, 02 delete, egr disabled, SRI, race header with small cat added. Alternator original and battery about 6 or so years old.

Any thoughts?
Am going to check terminals and reclean grounds soon plus will check for voltage drops.


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Old 11-15-2013, 11:10 PM   #2
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Manual Zetec idle should be about 700 rpm so nothing untoward there. If the car idles without missing, shaking or stalling, the lower the idle speed the better, otherwise you're just wasting fuel.

On my '01, I see 14.5 volts right at idle. When it did fall to 11.9 - 12.5V charging system ("battery") light came on intermittently during long idles and DTC P1246 eventually registered (but no CEL light came on.) Have you scanned for pending codes? Alternator failed shortly thereafter (intermittent output due to failed VR, I assume.)

If you have a tune, your tuner should be able to bump the idle if it bothers you.
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Old 11-15-2013, 11:49 PM   #3
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Thanks for the info. Will check the cables and terminals but it does seem like an alternator is likely in the near future.

Just had electrical gremlins and an alternator replacement on the wife's escape now right after the focus follows suit lol.
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Old 11-19-2013, 01:32 PM   #4
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Picked up a refurb bosch alternator, belt, and tensioner.
Gonna drive it a bit more first to see if it gets worse to verify it being the alt.
still no batt light or trouble codes scanned.

Today the voltage seems to have increased where driving or high idle is pushing 15v and hot low idle 13.2 - 12.2 but sometimes around 14.
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Old 11-26-2013, 01:58 AM   #5
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Never did get codes or batt light but did have to nurse it home keeping rpm above idle.

Replaced the alternator (what a PITA) and did the belt and tensioner since I was in there. Battery too since it was 6 years old or so. Solid 14.4 now even at idle. No more dimming lights or odometer light blinking with the turn signal at idle. I think the old alt was on its last legs for a long long time.

To get the alt out you don't need to move the engine. Bend the bracket the block grounds to and move the metal tubes clipped to the firewall. One unclips where it connects to a plastic tube.
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