Rough Idle / Spedometer Problems - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

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Old 09-02-2006, 12:01 AM   #1
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Default Rough Idle / Spedometer Problems


I am new to this forum and would appreciate any advice or suggestions.
First, Let me give you a quick background then I will get to the problems.

1992 Pontiac Bonneville SE, Currently at 67K Miles
Purchased car used two years ago at 60K Miles. Since getting the car I have changed:

1) Starter (2x)
2) Plugs, wires, pcv valve, air filter, fuel filter, periodic oil changes

Car was running good for two yrs and then the alternator died. Brought the car in to get an inspection and rebuilt alternator one month ago. After the car was returned to me, the problems started. Idle was rough and now the spedometer bounces all over the place. The mechanic also said he had a hard time getting the car to pass inspection and said he did something with the fuel timing. Not sure what was adjusted though.

Rough Idle/Stalling
Car feels like it is going to stall when sitting idle. It shakes more than it used to before I brought to mechanic and almost stalls out but doesnt. Only stalling that actually occurred was when I made a right turn on less than 1/4 tank of gas. And this stalling issue just started happening after getting car back from mechanic. Never had this problem or any kind of stalling issue since I got the car two yrs ago. Used to drive on or below 1/4 tank all the time, never had stalling issue before. I suspect that something that the mechanic adjusted is causing rough idle.
-Maybe something with the fuel pressure regulator? What do mechanics usually adjust
when trying to get the car to pass emissions inspection?

Spedometer Problems
The spedometer bounces all over the place. For example, when I drive and accelerate to 40 mph, when I slow down, the spedometer will still be bouncing around at 40. Other times, the car is sitting idle and the spedometer will just start increasing slowly. Also, this problem started after I got the car back from mechanic.
-Could the rebuilt alternator be causing this? Not sure of the brand in there now. There was an AC Delco alternator in there before.

I havent pulled any codes but I am going to attempt to get the codes with a paperclip. Once I get these codes, I will report back.


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Old 09-02-2006, 09:26 PM   #2
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Default Re: Rough Idle / Spedometer Problems

First of all, Welcome to the BC
Others will give you advice on the Stalling/Rough Idle issue.
I doubt it'* your alternator causing the speedometer issue
I had a similar problem with my Speedometer bouncing all over the place a few years ago. . I replaced the Vehicle Speed Sensor (VSS) and that solved my issue.
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Old 09-03-2006, 08:16 PM   #3
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you may want to check the ground to the alternator if at all possible.. i had a friend replace a starter on my car and he didnt tighten the ground wire bolt and it caused my car to have the same symptoms as you are discribing
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