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Old 05-02-2008, 11:49 PM   #1
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Default voltage drop and shudder

maybe someone remembers a post on this, im sure it exists:

When im sitting at a Red light for like 1 or 2 minutes i notice sometimes the RPMs drop to 500 then the engine shudders. the volt meter moves from below 14 (like 11 or 12) to 15 which is where the volt meter usually is.

if that made any sense, could someone tell me if i should save for a new altinator and perhaps what brand to get.

It'* just starting to get rather annoying thats the only reason i bring it up
118,000 miles now.
thanks
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Old 05-03-2008, 02:35 AM   #2
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my 03 does that sometimes, im not sure wat it is myself, and the mechanic at the GM dealer said that it wasn't anything too big.
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Old 05-03-2008, 10:32 AM   #3
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The alternator needs a certain engine speed to maintain voltage. If the motor slows below that speed, the voltage will drop. Address the idle problem first. Check all the vacuum hoses and fittings for deterioration, disconnects, and anything else that might cause a leak. Remove and clean the throttle body including the Idle air control pintle and passages. Carefully clean the MAF. If it has been a while, consider new plugs and wires.
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Old 05-03-2008, 12:10 PM   #4
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If the car shudders when the rpms dip, that'* not good. In my own experience, when a car dips the rpms while idling, it turned out being a bad cam sensor.

Does your oil pressure drop too?
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Old 05-04-2008, 06:31 PM   #5
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Default Agree !!!

Hey Guys,
I also have a 2003 Pontiac Bonneville SSEi.
Moved to Phoenix about 6 months ago and have an 18 mile commute to work.
When I take my exit in the AM and come to the first red stop light to wait for the green
The Voltage drops to 12 or 13 volt and RPM takes a "dip"
This may happen one or two times at other stoplights until I get to work.
I am also confused since the car runs perfectly otherwise !
Maybe the keyword here is "quick dip" it does not stall or anything bad.
My experience from owning many cars in the past would be a "fluke" since a Vacum issue
or otherwise would be consistent ?? Help ...Advice ????
Thanks,
Cabletek83
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Old 05-04-2008, 06:41 PM   #6
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Mine does this too. Always has. I thought it was the ac compressor kicking in or something.

2001 SE
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Old 05-05-2008, 11:46 AM   #7
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Default drop

Its more than likely a blurb in one of the sensor electrical connectors. Remove all sensor connectors including the ICM, clean the connectors and tighten up on the sockets, apply dielectric grease.
My 96 did this to me twice before I cleaned them, hasn't done it since. Its almost like someone turned the ignition off for a second then back on. The volts drop as the RPM does.
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Old 05-05-2008, 11:47 AM   #8
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The idle speed is controlled by a closed loop system using the idle air control motor. It is a separate air bleed in the throttle body that is opened and closed by the motor.

If you have idle speed variation, the thing I suspect is a dirty throttle body.

Of course you want to also confirm your plugs/wires are good. The motor could be chasing a rough idle for other reasons too.
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Old 05-05-2008, 01:08 PM   #9
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ive got my work cut out for me i guess...

the plugs and wires have 18,000 miles on them. i had to think. the MAF was replaced in February.

yes, my oil pressure drops too.
now what i havent mentioned is my rumble when i drive. when i press the gas sometimes..it depends on how hard, the car has a rumble to it.

could that be the source of the issue? the engine speed lowering so the volts drop. that would make sense if the problem is in the engine.

thanks
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