I know there is something wrong with my car I just cant figure out what. (typical female, I suppose.) I have an '08 chevy cobalt ls coupe. I've had a lot of problems with it, but recently I noticed my rpm's fluxuating, normally within the range of 1500 and 2500. I can feel my car almost chug along (speeding up a wee bit and then slowing up all within seconds and repeats until I put more pressure on the accelerator or brake.) It's trippy! I've always notices my rpm's plummet at random, mostly when I try to maintain speed. I've also noticed that when I let off the accelerator (on a flat surface) at lets say 45mph, it will continue at at least 40mph until I brake!! Not normal! It keeps speed like nobodies business.. UNLESS, after a minute or so of coasting, it kind of slows down a bit for a few seconds, and then bursts out almost jolting me forward back to the speed it was coasting at. It's hard to describe but if ANYBODY can let me know whats going on, I would MUCH appreciate it!!

when did you get it??

I got it in late january. It started doing this less than a month ago.

rpm's should not fluctuate at all. ..any check engine light?

Nope, no check engine light.

i have seen rpms fluctuate before if there was a spark plug issue. my dad's truck would run like a champ but when you came to a stop sign, the rpms would be at about 800 and then drop to about 3 00 or about 400 then go back up and down. and it would finally stall out. it turned out that there was a spark plug that was the problem.. maybe have that checked out. I also wonder if maybe it's not getting gas correctly. (if the fuel filter maybe a little clogged what with all the ethanol in the gas) I'd try putting a can of sea foam in you gas tank too. I'd do that first though b/c the sea foam is only about 9 bucks or so. did you get it from a dealer or a used car lot?? If there is ANY kind of warranty left on it at all, I'd take it to them now.

Without a check engine light on it's not a misfire, bad plugs on the car would make the check engine light flash. You will have to get a shop to connect a scanner and read the live data, one of your sensors are bad but within operating parameters so it's not throwing a code. Could be your mass air flow, it's an easy start, try cleaning it with a spray specifically designed to be mass air flow sensor safe and see if that helps. The check engine light wiil come on for a misfire before you even feel our notice the misfire happening.

hi friends, i have somewhat same problem. i have corolla 2008. my car's rpm fluctuates on idle between 0.3k-1k. engine makes extra noise. sluggish when going above 40km/h in 2nd gear . low pick and low power. changed plugs, throttle body cleaning but same problem exists and their is no engine check light on running engine. what is the possible problem?

My 2009 Chevy Cobalt started doing something similar a few weeks ago. When I start it up the RPMs fluctuate (500-1000) and when I start going (forward or reverse) the car randomly speeds up and/or slows down with steady pressure on the accelerator. I only have issues the first 1-3 min. of starting up the car…then it goes away. Very strange and I'm concerned something might be going out on the car…as if something was clogged, I'd expect this to happen the whole time the car is turned on. I bought the car brand new and it has 68,000 miles. Any thoughts?

i'm having this problem with my 08 Chevy cobalt LT... and i just bought it a week ago. I think it may be the fuel pump or the fuel pump senor either one.. my Chevy rpm will fluctuate when i'm near 30-45. I just give it alittle bit more gas and it stops.

Garrett have you resolved your issue? Or momonnie? I just purchased my 08 LT coupe and my situation is identical.