Odd electrical problem - 2006 Chevy Cobalt

[ChanceTheRapids]

Have an issue with the wife's car. Trying to sell it but need to resolve this issue first.

When I first start the car up after it's sat for a while, it's not uncommon for it to die once or twice in the first 10 minutes of driving. I can be driving 50 mph down the road, come to a stop at a stop sign, and poof, dead. I just put it into neutral/park and it starts back up every time.

I took it to the shop and they said all the electrical checked out. Didn't make any sense. Could be because I had driven it for ~30 minutes before going up there, though?

So the main issue other than it dying is, I will pull up to a signal light or stop sign and the car will really bog down; the RPMs will drop fluctuate from ~250-~700. After a second it equalizes and holds steady at it's normal idle, but it takes a little bit. In classic low-battery fashion, the lights will dim when the RPM drops as well.

I wanted to say battery, but the guy said it checked out. I thought maybe Voltage Regulator, but low/fluctuation voltage would have probably shown up in the battery test.

I'm lost. Any ideas?

[JawjaBoy]

Its possible that your alternator is bad or not getting a good connection. Unhook the battery while its running and see if it runs/sounds different. If the alternator is working properly, it will keep running but if not it will shut down.

[HuskyBoris]

electrical problems can be a real headache but my best guess would be a short in the ignition system like 2 wires rubbed through and shorting on each other or something similar.
Cobalts also had a recall or a technical service bulletin (can't remember which) on the ignition switches themselves but I am ot sure if it was an electrical problem or not,I'll check Monday ,, I work at a Chevy dealer so the info will be available .just to be curious did you check the pwer fuse on the battery to make sure it's tight?.sometimes the prongs shrink so to speak and if you hit a bump just right it'll shut ya down,,so many things it could be though,these kind of problems can tricky.

[OkieDavid]

Daughter has an 09 Cobalt. That car has presented a myriad of electrical "burps" the likes of which I've never seen. Recall was for the ignition switch. Ours went out one week BEFORE we got the recall notice. Dealer let me know while I was sitting in the lobby waiting for them to fix it. Seems to also have an issue with the battery terminals loosening. I think it is due to the extra vibrations that come from putting the battery IN THE TRUNK.....Yep, I did say that. The battery sits right beside the spare tire. Figured that one out the first time I had to drive out had jump start it. Tuned out the battery was fine and just had a loose terminal.

We've dealt with dim lights at stop lights and engine bogging. Seems to happen just before I have to re-tighten the battery terminals. My only advice would be to start there and work outward.

[agmantoo]

If the fuel filter has not been changed recently I would replace it. At idle and the output of the alternator not high the fuel pump could have a problem pushing the fuel through a dirty/clogged filter.

[ChanceTheRapids]

Thanks for the tips everyone. Replaced the fuel filter but still kind of sounds the same (it did need to be changed though). The fuses and terminals were all nice and tight. I'll look more at the alternator tomorrow.

[jamesdaclark]

Your symptom is very common with a dirty throttle body. Over time oil residue and grime will build up where the throttle blade comes closest to the throttle housing. The air gap that is supposed to be there gets smaller. This air gap is a portion of how idle speed is controlled. Remove the air intake boot at the throttle housing and hold the throttle blade open with your finger, you will be able to wipe the entire area clean. DO NOT spray carb clean in the throttle, it can cause the throttle position switch to short out. Spray the carb cleaner on a rag and use that. It may take a few minutes of idling after that for the engine control module to relearn the idle speed.

[foxtrapper]

If it's really dropping that low at idle, the lights will dim. That's normal and to be expected. It indicates nothing bad about the charging system or the battery.

I suspect you've a problem with the idle air motor. That is the component that maintains idle speed. It's a bypass around the throttle plate that regulates the amount of air coming into the intake of the engine. More air revs the engine up, less air brings it down. It is supposed to move to hold the engine rpm steady, and compensate for the changes in load on the engine.

You can test the idle air circuit by doing things that create a load. Turn on the A/C, turn the steering wheel, etc. The engine should drop a bit as the load first hits, and promptly recover without wildly overshooting.

Idle air motors do get dirty/sticky, which causes them to not move. Then engines stall. Cleanable with solvent, but beware of floating dirt further into it.

Dirty throttle plate that doesn't seal properly can confuse the idle air circuit. Easy job with a rag to wipe it all clean.

A dirty MAF sensor will also cause problems, which can include stalling and low rpm. Cleanable with a can of MAF cleaner. I don't really recommend hitting it with other solvents, or a rag.

[ChanceTheRapids]

HUGE thanks everyone!! The throttle body was disgustingly dirty, and cleaning it up (a 10 minute job) fixed the issue! The car funs fantastic now.

:-)

[jamesdaclark]

The best repair is the free repair.

[HuskyBoris]

Originally Posted by ChanceTheRapids

HUGE thanks everyone!! The throttle body was disgustingly dirty, and cleaning it up (a 10 minute job) fixed the issue! The car funs fantastic now.

:-)

glad you got it fixed,I did look it up on the GM computer at work but didn't come up with anything concrete or common then one of the techs told me about cleaning out the throttle body but James had already told ya that by then,sometimes the fix is just plain simple