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4.9 sudden high idle question. by Frizlefrak
Started on: 11-07-2007 12:36 AM
Replies: 3
Last post by: Fieroking on 11-08-2007 01:06 AM
Frizlefrak
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Report this Post11-07-2007 12:36 AM Click Here to See the Profile for FrizlefrakClick Here to Email FrizlefrakSend a Private Message to FrizlefrakDirect Link to This Post
My 4.9 / 4T60E combination has performed flawlessly for about 2000 miles now....until this past week. I drove it across town and back, and it developed a very high idle / very rich condition. As I suspected, the vacuum line between the throttle body and fuel pressure regulator had split and come off. I replaced the line, and fired it up. Still had both issues.

After some serious head scratching and hooking a vacuum gauge to the car to rule out any further leaks, I decided to pull the fuse to the PCM to reset it. The problem went away and it runs perfectly now.

Here's my question.....I,m using the original chip, so I don't have a check engine light or a way to scan for codes right now. I figure it set and stored a code when the leak developed....but shouldn't the PCM have corrected the high idle by itself once the leak was fixed? Or was "rebooting" the PCM necessary to allow it to relearn the proper idle speed?

I think Santa Claus needs to bring me a nice scan tool for Christmas....

T.I.A.
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arte444
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Report this Post11-07-2007 01:20 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Direct Link to This Post
You could make sure the ISC isnt malfunctioning by retracting it and unplugging it. That might fix the idle but not the rich condition. I've heard of some people eating o2 sensors also.

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-Kyle
Email: kakagiraffe@gmail.com
Aim: Littlechugger
1988 Notchback 4.9 V8, 5spd Isuzu
True Dual Exhaust, Delta Cam
1993 Ford Probe 5spd

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Frizlefrak
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Report this Post11-07-2007 08:36 PM Click Here to See the Profile for FrizlefrakClick Here to Email FrizlefrakSend a Private Message to FrizlefrakDirect Link to This Post
Arte...thanks.

OK...the plot thickens. I drove the car to work today and it started acting up again....idling around 1800 rpm in park. Tried resetting the computer, didn't work this time. On the drive home, I didn't even have to keep my foot on the pedal on the freeway.....until about halfway home, when everything returned to normal. I pulled into my driveway, and she's idling at 650 in drive and about 850 in park.

So....I have no vacuum leaks, and an INTERMITTENT high idle. Where should I start looking? Coolant temp sensor? Any good way to test the CTS without replacing it? ISC motor?

I understand there is an "idle learn procedure" on the 4.9. I've never done it, but have been driving the car for a year now with no idle issues until just recently.

Any ideas?? +'s handed out liberally for all with ideas.

Dan
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Fieroking
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Report this Post11-08-2007 01:06 AM Click Here to See the Profile for FierokingClick Here to visit Fieroking's HomePageClick Here to Email FierokingSend a Private Message to FierokingDirect Link to This Post
You might want to check your O2 sensor. I had idle problems with my 4.9, I replaced the Bosch sensor with one from the GM dealer and the problems went away.
Hope this give you some help

Joe Sokol

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85 SE Daily driver
88 Formula/GT 4.9 Allante Intake (My Baby)

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