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Discussion Starter #1
Hello. I am new to this site and was wondering if someone can help me? The dealerships can't! I own a 2008 G6 Value Leader with the 4 cylinder engine in it. The real issue I have with this car is it feels like it surges driving between 30 and 55 miles per hour. Also very strange is that when your cruising at 55 the tach will go up 200 to 300 RPM's and then go back down to normal. It will keep doing this throughout the drive. You can hear the engine speed go up but the car doesn't move any faster. I've taken the car to the dealership 3 seperate times and they say it's normal. Anyone else this this issue? Thanks, Don
 

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I can honestly say while cruising at a steady speed, my RPMS don't move up or down. Even if i have my foot off the gas and I'm just coasting.

I too have the 4cyl. How many miles on your car? It sounds like a transmission issue, Like it's slipping or something

If it has a lot of miles maybe consider cleaning the Throttle Body and checking the spark plugs just to see how they look. You can read how the engine is running...


I figure these are good steps to take to at least determine what issues you may or may not have. I don't know much about transmissions but it could be a bunch of different things...
 

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Ah, I see. Well then you can disregard ALL of that... haha

But I would say take it to your dealership, and take the service writer for a drive. Point out what it's doing and make it clear to them. Or have them drive and point it all out to them.

If you feel up to it you can check out your air filter and throttle body. Even look at the MAF if you want. the MAF sensor shouldn't be dirty. But the TB could be. Mine was pretty dirty at about 31k

It could just be the right amount of gunk in the right spot. You can get Throttle Body cleaner at any auto parts store or even walmart and such. Just follow the can's directions.

Or just take it to the dealer, Your car should still be covered by the powertrain warranty, which is where your problem is

good luck!
 

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Throw some seafoam through the PCV vaccuum and oil crankcase and some Techron in the gas tank. Clean those fuel injectors!

This kind of problem is hard to diagnose. It's not hurting the car either.
 

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Sounds to me that the torque converter clutch (TCC) could be cycling on and off. Do you experience the surging when the cruise is on? Does your road speed vary when it is surging? Most GM cars are set up to cycle the TCC off when you step on the brake. You may notice if you are cruising at steady speed and very lightly apply the brake, the tach rpm will increase when the TCC cycles off and then decrease as the vehicle speed slows. The increase should probably be less than 100 rpm or so, but your tach reading may not be so precise in this situation. Could it be a "false" brake input causing the TCC to release.
 

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Discussion Starter #7
I do not cruise control on the car. It's just when you are going an even 55 MPH down the road for many miles you can see that tach rise up and down about 300 revolutions while driving. You can hear the engine increase but the car doesn't move any faster. I've been working on cars since I was 15 and drag raced when I was younger so I much about cars. It's this new stuff I don't know anything about. I've never had a car with the tach moving on it's own UNLESS I'm doing it myself.
 

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Sounds to me that the torque converter clutch (TCC) could be cycling on and off. Do you experience the surging when the cruise is on? Does your road speed vary when it is surging? Most GM cars are set up to cycle the TCC off when you step on the brake. You may notice if you are cruising at steady speed and very lightly apply the brake, the tach rpm will increase when the TCC cycles off and then decrease as the vehicle speed slows. The increase should probably be less than 100 rpm or so, but your tach reading may not be so precise in this situation. Could it be a "false" brake input causing the TCC to release.
I should have mentioned that the TCC is also released when you increase throttle position. Sometimes you can see this if you barely increase pressure on the throttle pedal, the TCC will jump up a bit without increasing vehicle speed So it could also be some sort of false throttle signal causing your RPMs to jump.

Does it jump back and forth constantly? Once or twice and settle down?
 

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Discussion Starter #9
The strange thing is it doesn't do it all the time. I drove it one morning last week to work and it ran like a new car. Then on the way home it was totally different. I also remember another issue on that same trip home that the car acted like someone put the brakes on because the car slowed down on it's own and then regained power. After that it ran like crap. On Sunday I took it for a 1/2 hour drive and all well again. I still think something is wrong with it but the dealer tells me it's normal.
 

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The strange thing is it doesn't do it all the time. I drove it one morning last week to work and it ran like a new car. Then on the way home it was totally different. I also remember another issue on that same trip home that the car acted like someone put the brakes on because the car slowed down on it's own and then regained power. After that it ran like crap. On Sunday I took it for a 1/2 hour drive and all well again. I still think something is wrong with it but the dealer tells me it's normal.
The tough thing about most of these problems is that they tend to be intermittant.....and of course they usually don't act up when they are at the dealer. It's fairly easy to find and fix a problem if it is repeatable. Do whatever you can to pinpoint when it happens (speed, warm/cold, certain stretch of road, uphill/downhill/flat, increasing/decreasing speed, etc.)
Try another dealer, that does not sound normal to me. Did they say they experieced the incident?
 
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