08 Grand Prix

[carp master]

I am not one to post on here much but I am always "Lurking in the shadows". Anyway I have a question about a Grand Prix I bought a few years ago. When I first acquired the car it would up shift into the next gear as soon as you stepped on it fairly hard making for a rather uneventful and slow accelerating process. I figured this was normal as it was the only thing I found unusual. Then after awhile it begin to shake subtly when accelerating in first and second gear after second gear it would accelerate flawlessly. in the last few months it has begun to develop a fairly bad jerk when stopping and then going again. This ONLY happens after driving long distances. It never happens if I drive under 100 miles .Also it only happens about 1/3 of the time after driving these long distances. It will still accelerate slowly until about 3 mph and then it will jerk fairly hard when it does happen. Any Ideas what would cause this? The long distance thing is what confuses me.

[Jeremy airjer W]

It sounds like you are describing a transmission slip in first gear?

how many miles on it?

Is the check engine light on?

Have you checked the transmission fluid level and condition?

[Mike89]

I was thinking sensors maybe too

[bullhead master]

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Edited September 29, 2016 by bullhead master

[carp master]

So apparently I have two accounts both made in 2009 as you can see by the "-" post above. I don't understand how that happened as they are both under the same email... and both have the same password.. anyway it has about 126,000 miles on it and the check engine light is not on. I have checked the fluid and it is full. I had the transmission flushed when I bought it at around 80,000 miles. It only shifts hard when going from a complete stop and will only shift hard in the first 3 or so seconds  when taking off from a complete stop.. Otherwise it will occasionally shake very slightly when accelerating in first or second gear. It doesn't shake hard but it is noticeable. Thanks for the help.

[Jeremy airjer W]

I am having a hard time figuring out what the symptom is myself. There is no "shift" from a dead stop. It either goes or it slips and then bangs into gear after 3 seconds.

[delcecchi]

OK, just from what I am reading and never having been to mechanic school....

Is it possible that when the car comes to a stop that the transmission doesn't, for reasons unknown, downshift to first but stays in a higher gear?  Then when starting out after a few seconds it does downshift to first with a jolt?  Being in too high a gear would account for the slow acceleration and the downshift would be the jolt.  Staying in too high a gear would make a shudder maybe. It did in my old stick shifts .

[Jeremy airjer W]

2 minutes ago, delcecchi said:

OK, just from what I am reading and never having been to mechanic school....

Is it possible that when the car comes to a stop that the transmission doesn't, for reasons unknown, downshift to first but stays in a higher gear?  Then when starting out after a few seconds it does downshift to first with a jolt?  Being in too high a gear would account for the slow acceleration and the downshift would be the jolt.  Staying in too high a gear would make a shudder maybe. It did in my old stick shifts .

should trigger a check engine light....

[delcecchi]

Oh yeah.  I keep forgetting about all that modern computer stuff in cars.   So the computer would notice the tranny didn't shift all the way down as the car stopped?     There goes that theory.   

And why only after a couple hours of driving?   Some sort of overheating of the transmission fluid?  cooler plugged in the flush process?   

Here is a question for Carpmaster..... Is it different in the summer vrs winter?   Like you only have to drive 50 miles in summer and 200 in winter?  

You guys that actually know can feel free to ignore my suggestions if you don't want to waste time answering.  

[Macgyver55]

 My guess is there is a worn bore in the valve body.  I actually had this similar problem on my wife's car. (06 Impala)  When taking off from a stop it would try to go slowly then would lunge forward as if someone rear ended you.  Was very erratic and unpredictable  but grew worse with time.  Luckily for me (readily admit I'm no transmission guy). I have a neighbor who is a transmission specialist who called it right from the start and said it's quite common on this particular transmission.  It never set a code on our car either.  The valve body was removed and the bore was drilled and sleeved and worked perfectly afterwards. 

[PurpleFloyd]

A few things.

Could this be a side effect of the lower intake manifold needing a new gasket? Secondly, If a catalytic converter is plugged it can cause symptoms similar to trans issues as the car can shake and be sluggish.

[fishingstar]

my sons 02 had transmission problems not quite the same but it was a valve body rebuild that fixed it. 

 

Edited October 2, 2016 by fishingstar

[Jeremy airjer W]

On 10/1/2016 at 7:44 PM, PurpleFloyd said:

A few things.

Could this be a side effect of the lower intake manifold needing a new gasket? Secondly, If a catalytic converter is plugged it can cause symptoms similar to trans issues as the car can shake and be sluggish.

lower intake would be unlikely.

A plugged cat would give a loss of power and if bad enough can delay a transmission upshift. Typically first gear is fine and becomes more noticeable as you try to accelerate, especially up an incline.