tribal_sun

When I go to start it up, sometimes the engine will rev up and down from 500 to 1200 rpm irratically, and then level itself out. Sometimes it does it when I slow down at a light or stop sign. I have a 2005 stock coupe stick shift. And recently it has begun to stall when it does this.

-I pulled the plugs, ac delco stock, and they were white. Thinking the mix is too lean. Replaced with Bosch 4+ to see if that solved the issue. It didn't.

-Checked the air filter, its clean.

-All hoses and electrical connections in the main engine compartment are fairly clean and connected, as well as i can tell with a clear day and a flashlight.

-Battery is 4 months old.

-It throws no codes whatsoever.

-I tried to re-teach the PCM by unplugging the battery for 45 minutes to wipe the memory and drove about 60 miles, thinking it would re-learn and "forget" a faulty protocol it might have picked up. That didn't help either.

-All related fuses are good on the side passenger compartment and under the hood.

I have this hunch its an electrical issue, but cannot pinpoint the problem. Haynes is pretty vague on this issue too. Ironically, it never starts acting sporadically when I take into the shop, or when I show someone else the car. Now mind you everything is stock, I want to mod this car, but want to get this problem figured out first. I didn't want to do an overhaul unless I absolutely had to, and was hoping that with all the info I provided one of you might say "Yeah ok, its this this and this, here's how to fix it." Any and all help would be awesome. Thanks.

MikeyB

This is a very common issue with cobalts, pretty much everyones does it, clean your throttle body. That fixed my issue, but some it doesnt.

BlackJackSS

iTrader: (2)

mine was spark plugs... made the car feel brand new again when i changed them... also did the fuel filter too.

blackbolt89

mine still does it and i cleaned the TB, changed the plugs, and the fuel filter. i've given up on the issue. just as i have with the rattles and steering column. as long as the car doesn't completely give out when it "lopes" then im fine.

BlackJackSS

iTrader: (2)

just tell everyone you got a nasty cam

BLKLS

Take notice if the ac compressor is on when it does this. Mine did that and i have heard of others that did that to. They have a ecm update avalable to correct the issue.

tribal_sun

Ok so I thought I fixed it. Like I said before I changed the spark plugs to Bosch +4s, and that didn't help. Had a dealer look at it and couldn't find anything (not surprised). They did provide a software update for "lock" -ed radios.

Then one morning it didn't want to start. Every once in a while the car won't start on the first turn and you gotta hold the ignition a moment but then it lights up fine. This time it stuttered and slowly choked to life. There was a smell of burnt rubber in the cabin and no acceleration at all. Also, there was a weird mechanical sound when I tried to use the gas. I was told it was really loud too. I drove it to my friend's garage with a flashing engine light and told him everything that was wrong with it. Come to find out, it was throwing three codes, oil pressure, fuel pressure, and ignition. I guess the cause of the problem was a faulty ignition module. My friend told that would solve all my engine loping problems so I paid out for the repair. That was two weeks ago.

Same thing happened this past Saturday, SAME symptoms. Took it back to the shop and found out it was the ignition module again. So he replaced it for free. Now I'm at a crossroads in thought. It could have been a truly faulty ignition module, or its something else causing these problems.

Everything I've read indicates fuel system or air intake. I don't think its the fuel pump, or intake, and the air filter looks clean. I'm suspecting its either the injectors or fuel filter. I just don't want to change out the injectors until I hear some good advice or concrete evidence that is the problem.

Sorry for the novel but I'm trying to be as specific as possible to pinpoint the issue and fix it. Any and all help is greatly appreciated. I want to mod the paint off this car, but want all this stock stuff taken care of first.

copson20

have the dealer datalog it. they can check to make sure the injectors/ fuel and/ intake are working. best way to do it. if they tell you they cant, they lie!

06_ion2

Any mods? seems like a vacuum leak

TCguy

thats what i was thinking

RedBaseBolt

My car's done this since day one. I've learned to live with it.

tribal_sun

No mods, and everything I've read refers to a vacuum leak. To be completely stupid though, I'm not really sure what that means.

[ANOTHER UPDATE]:

It finally threw a code, 420. Ironically this means the Catalytic Converter is shot. I took it to the dealer to have replaced, and unfortunately it still lopes. I'm buried in snow right now so I can't really do any diagnostic work on it, when the spring comes and it starts to get warmer I'm going to take off the air intake and clean out the throttle body and get the fuel filter replaced. Thanks for all the feedback on here, it's greatly appreciated.

tribal_sun

scrubbed out the throttle body with some CRC cleaner. 50 miles and so far so good.