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Old 05-17-2001, 06:54 PM
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Join Date: Jul 2000
Posts: 97
Last week I had a dead battery in my '85 380se. I jumped the battery and took the car to my tech, who diagnosed a faulty alternator and replaced it. My question is after the jump, the car idled very high and has continued to do so. It idles around 1500-1750rpm. Is this related to the alternator or is it a coincidence? What could cause this? The car was fully tuned 4 months ago and ran fine until last week.

Jack Mac
85 380SE 95K
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Old 05-17-2001, 11:17 PM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
or maybe the overvoltage relay, check fuse.
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Old 05-18-2001, 08:38 AM
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First check the connection and wiring to the Idle Air Valve to be sure it wasn't pulled off or damaged. The high idle is exactly what you get if you unplug the idle Air Valve unit. If not, perhaps it is the idle control module. Good luck.

85 500SL Euro
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Old 05-18-2001, 12:35 PM
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When I brought it in for the alternator, the tech checked the high idle. He said they couldn't find anything wrong and that it went away if the car was running for a while. The high idle is only when the car is in park (I should have mentioned this before) but goes away when you put it in gear.
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Old 05-18-2001, 01:25 PM
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Join Date: Jul 2000
Location: Sunny Florida
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The OVP fuse would be my first check. If this is good, check the throttle position switch.

This switch is at the base of the throttle, which tells the computer you are off the gas and should be idling. Check it for continuity when the gas pedal is released. The switch is buried down low in the throttle on the intake, but the leads plug in at an easy place to access. The car will idle high, as it is trying to idle on the "run" circuit.

[Edited by JohninFla on 05-18-2001 at 01:30 PM]
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)
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Old 05-18-2001, 01:48 PM
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Join Date: Jul 2000
Posts: 97
Thanks for all the replies. I suspect the fuse might have blown when the battery was jumped. That's the first thing I'll check.

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