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Old 08-17-2011, 10:59 AM   #1
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Default 2005 Grand Prix SE Issues

Hey Guys,

My girlfriend has recently picked up and been driving a 2005 GP SE. Recently, she has brought up a couple issues to me that I wanted to run past you guys for advice.

First of all: She has complained her gas mileage has been getting worse. I have Aeroforce Scangages installed on my car, so I plugged them into hers and was scrolling through the options. The car didn't throw any codes, but oddly enough, at idle (roughly 800 rpm) the gage was reading 8 percent throttle. I found this kinda odd as I thought it should read 0% since no throttle was being applied..kinda like my car. When the car is reved, the throttle percentage jumps up, then right back down to 8 percent...could this be related to a bad throttle position sensor? How costly or intensive is this to replace?

Second issue: sometimes when starting, it sounds like the car starts and then stalls out. If she turns the key a second time, it starts right up and runs great. Didn't know if anyone had any suggestions for this....the car is REALLY quiet when starting, and sometimes maybe the key isnt being held long enough....not sure...any suggestions is greatly appreciated.

Thanks guys!
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Old 08-17-2011, 12:09 PM   #2
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i would put a fuel pressure gauge on it see if the pressure is good and holds. im kinda thinking fuel filter or pressure regulator

sometimes they start hard when the plugs are starting to go too, how many miles on the car?
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Old 08-17-2011, 01:56 PM   #3
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Hey JW,

I will prolly replace the fuel filter since its an easy fix and only costs like 5 bucks.

The car currently has about 78000 miles on it. She purchased it about 3 months ago and I think the car had around 76000 on it. We dont have any records of the previous owner, so I wouldnt be surprised if the plugs and wires are factory. I will also go this route and throw them in and update others.

Thanks for the reply!
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Old 08-17-2011, 03:32 PM   #4
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Her car is drive by wire. There is no IAC valve to control idle. Idle is controlled via the computer opening the throttle plate. Afterall idle is basically a controlled vacuum leak to get air.

8 Percent seems high to me, I don't have expected values though.
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Old 08-17-2011, 04:08 PM   #5
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Pull the vacuum hose off the fuel pressure regulator and smell it, bet you smell gas.
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Old 08-17-2011, 09:57 PM   #6
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Hey Danthers,

If I do smell gas when the vacuum line is pulled from the fuel pressure regulator, what will this mean? What has failed?

Thanks!
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Old 08-18-2011, 12:33 AM   #7
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It means the FPR is bad and leaking raw gas in to your intake manifold.
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Old 08-18-2011, 08:16 AM   #8
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You don't have to worry about checking the fuel pressure regulator and it'* vaccum hose.

Because you don't have a pressure regulator on the rail.
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Old 08-18-2011, 08:42 AM   #9
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He doesn't? Well dang.
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Old 08-18-2011, 01:21 PM   #10
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He doesn't even have a fuel return line, because it doesn't have a regulator, it doesn't return excess fuel.
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