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Hey guys, just stopped in to ask a question. I have an 08 Cobalt LT, when driving between 30 and 35 when im cruising and lightly pushing the gas the RPM gauge will surge up and down very lightly, its not super noticeable, still annoys me though lol. Appreciate in advance. Also one more thing, why do base models only have 4 lugs and mine (LT) has 5 lug?
 

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You're not the only one who has this surging around that speed. It's just the way it is. Might be the torque converter not wanting to make up its mind if it wants to lock up or not. I'm up to 204,000 miles, so it must not be a huge issue.
 

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It's fairly normal unfortunately. I'm at 199,000 miles right now and mines been doing that since around the 120k mile mark lol. I had a transmission shop look into it and they determined it was not a transmission problem. Was told it is often caused by carbon buildup in the combustion chamber. Might be plausible, at 100k miles the Piston tops were very clean when I changed the plugs. At 150k miles there was a considerable amount of carbon. The surging hasn't gotten any worse so I may do a top end cleaning sometime.

Interestingly enough I had a rental hhr in 2009 or so and it did the rpm surging and it had less than 30k miles on it and I'm sure it had a diet of the cheapest crappy gas the renters could find. Basically the computer is telling the torque converter clutch to cycle on and off based off of the calculated load on the engine. The carbon build up changes the pressures in the combustion chamber and then causes the computer to start giving funky commands.

It's also possible you have a bad torque converter but in my experience if you have a bad torque converter it will get bad rather quickly (previous vehicles I've driven).
Also, it's been a long time since I've seen the info published but I think 2007 was the first year non SS models could get 5 lug hubs. 2007+MY's you could get a 1LT or 2LT package. 2LT's came with 5 lug wheels and a few other items.
 
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