Hope some of you car-savvy dopers can help me out here. I have a 2002 Chevy Malibu with about 130k miles on it. A few weeks ago, it began giving me trouble that I’m hoping I can fix myself without taking it into the shop.
Here’s the problem: when I pull up to an stop and idle, the car stalls. It seems as if the car is idling very low. I was thinking maybe the idle just needed turned up a bit, but it doesn’t happen all of the time. It happens most often when the engine is cold and after the car has warmed up a bit, the problem mostly goes away. Also, it seems to be more of an issue when it’s humid out though that might be confirmation-bias on my part.
So, from what I can tell - there are a lot of reasons this could be happening. My goal is to try and fix the cheap potential causes first. I’m fairly handy and don’t mind getting my hands dirty. I just don’t know where to start.
Anyone have ideas on what this could be and where I should start to fix this?
Has it ever had a tune up and/or new spark plug wires? If it’s never had them, I’d go ahead and do new plugs and wires since it’s probably just about due anyways. If it has had the wires replaced, check that they’re snug.
If that doesn’t solve the problem, the sensor I’d scrutinize is the coolant temp sensor. If you have a service manual and a volt-ohm meter, there will be a way to test it, or else coolant sensors for GM’s usually cost something like $10-15 so it might be worth just trying. It’s generally a pretty straightforward job, though you may have to drain the coolant a little depending on where it is.
If that’s not the problem, the idle air controller would be the next thing to check, but I think that if that were the problem the check engine light would be on.
It’s been a couple of years since it’s last tune-up, and I don’t know if they changed the sparkplug wires at that time. I’ll look into doing this to see if it helps.
The fluid levels are all decent. I’m pretty good at keeping an eye on them. The car isn’t overheating, just doesn’t want to stay running when the engine is cold.
What type of ignition system does it have? Those are pretty classic symptoms for a cracked or leaky distributor cap. Of course this would require that you actually have a distributor.
Bad spark plug wires or old plugs (like GreasyJack mentioned) would be my second guess. Take a spray bottle with plain water and spray the spark plug wires at night. if you see a pretty light show then you need new wires. If you’re at 130k on the original wires just replace them anyway (and the plugs). If they aren’t the problem they will be soon. Be very careful to route the new wires in exactly the same place where the old wires went.
Is there any sort of hissing from the exhaust or any other sound that would make you think the exhaust is being restricted? I had the honeycomb inside the catalytic converter in my truck basically fall apart, which stuffed up the exhaust and made it idle rough and want to stall. Any sort of exhaust restriction can cause you problems.
On a modern fuel injected car, you shouldn’t ever have to adjust the idle. The computer controls the idle speed with the Idle Air Controller which is a stepper motor that moves a pintle back and forth to control the amount of air being let into the intake. The sensor it mostly uses to decide how much air to let in is the coolant temp sensor, since the engine needs more air when it’s cold. There still is a stop screw where you can manually increase the lowest possible idle setting, but this is just covering up the real problem.
The idle can be rough or erratic because of tuneup issues or a vacuum leak or a plugged exhaust like engineer_comp_geek said, but these would cause drivability issues and/or trip a check engine light on an OBD-II car. If the idle issue is the only symptom, a CT sensor or IAC are the most likely culprits. Also, I believe if the computer tries to change the idle with the IAC, but it doesn’t change that’ll trigger an OBD-II code too, so I’d say the CT sensor is the most likely culprit.
First thing I’d do, after a visual check for the obvious (e.g. broken/loose vacuum hose), is to inspect the throttle body for carbon build-up and (as needed) clean it thoroughly.
I see that a CT Sensor is only about $12 at the local Autozone. I think I’ll give that a shot.
The IAC Valve looks like a bit more work (and money) so I’ll try that last.
Also, I may as well change the spark plugs and wires - but I’m a bit daunted by the back three plugs. I think they’ll be pretty hard to get to and I might be better off having a mechanic do it for me.