Rough Idle Problem-Alero

I bought a 1999 Olds Alero. I bought it because I've always had good luck with Oldsmobiles, I've had a '91 Cutlass Calais, '89 and '92 Eighty-Eight, '86 Ninety-Eight, and an '84 Cutlass Supreme. All great cars. But I digress.

The car runs superbly when driving, but it idles down to 500-750 rpms after being stopped dead still for about 2-3 seconds. Fuel economy is not really what I expected, but I do not know what its supposed to get. I've been measuring it religiously and it gets 22-26 mpg depending on how much traffic I run it through.

I was told the engine (2.4L Twin Cam) was replaced. The car has 106k miles on it. I have replaced the spark plugs and their connectors, replaced the throttle body and Throttle Position Sensor, Idle Air Control Valve, and fixed misc. vacuum leaks. I have also replaced the air filter, and oil change. The car used to stall after it idled down, now it continues to run, but still the idle problem persists. I've been told a myriad of things from the Catalytic Convertor, The Fuel Regulator, Balance Shaft Bearing failure or shaft breakage. Does any of this sound like it could be the mystery problem? Any ideas?

at idle, you can move the trottle just enough to get it to idle at 1000-1200 rpms and it seems to like running there. Can't figure out why it idles down so low.
I'm about at my wits end to figure out what it wrong. Any help is greatly appreciated!

Will

Your 2.4 should idle around 600-650rpms.

Is it just idling low or is it missing out or anything?

Could just need it tuned through the electronics(pcm) which any decent shop should hav on hand for such purposes. Or you could purchase one for a few hundred dollars.

Hav your tried any injector cleaners in a while?

Dirty fuel filter, dirty injectors, and or faulty FP regulator could also cause low idle which is rough or missing out.

Also 22-26mpg is pretty darn good. Should be better than any other Olds you've owned :)

Hope this helps!

This post actually made me register here.

Anyway, I have a 99 alero with the 2.4 and have the exact same issue. It has never had stalling problems.

What happens to mine is that after the car warms up it starts to get the rough idle, but this only happens when it is in gear, it idles smooth as day when it is in nuetral or park. When the car is cold the problem is not bad either.

The car feels like it is "Pulling" when it is donig this. If i bump the rpms up 100 or 200 rpm it smooths out. My idle is around 600 or so.

One thing I have noticed is that it runs a little warmer then it used to when i first got it, I bought the car in 1999 and have had almost no problems with it since. (I have 141,000 miles on it)

Does anyone know what the temp guage readings are in degrees, mine is jsut over half on the guage, but i do not know what the coolant temp is at that reading, I was wondering if replacing the termostat would help a bit, it used to run a bit under half on the temp guage.

Anyway one of my coworkers mentioned to check all the vaccuum lines. Other then that I am at a loss.

I ran through a "complete fuel system cleaner" that is supposed to clean the injectors, combustion chambers, and valves. It has helped some. I had a friend of mine that went to college for auto repair look at it, and he cleaned up the intake manifold and gasket, set the idle up some, and it now does not die at idle. Still idles rough, though. He said that the motor that was put in it is an older version of the 2.4L, and may be causing a little problems. he said also that the gasket between the exhaust manifold and the pipe is leaking. He said that could be causing a miss in it (most of the roughness). He checked the fuel regulator and said that it is working properly.

Btw, my Cutlass Calais got 32 mpg (2.5L Tech IV engine) and my 1989 Olds 88 got 30(3800 V6).

Thanks for the help!

Your problem is similar to mine it sounds. Mine does seem to run hotter than cars ive had in the past, but the gauge reads normal. It does run above half on occasion, esp. in traffic. Seems to be a quirk in the car, as I have flushed the cooling system and replaced the thermostat. I wouldn't worry unless it causes you a problem or gets worse with time. As for the idle, I would try the idle speed setting on it as I did. Hope this helps.

I am not sure if this is happening for you but i am starting to think i should be blaming the Tranny on the problem for me. The other day I thought about it and did some testing.

When the car is in Park or Neutral it is smooth.

When the car is in reverse it is smooth (I didn't realize this at first).

When the car is in Drive (or any forward gear) it is rough. I wonder if replacing the tranny fluid would help, or if running some "mechanic in a can" would help things out.

To me it is odd that the car is smooth in reverse and rough in drive, as in both situations the car is in gear. And by rough i do not mean it is engine roughness, it is more of the whole car vibrating like the car is trying to Pull.

Cooter2, sounds like you may hav a TCC going out on your trany.
Might take it to a shop that can scann for trans codes, and see if any come back.

Cooter2, sounds like you may hav a TCC going out on your trany.
Might take it to a shop that can scann for trans codes, and see if any come back.

Thanks for the tip. But i was doing some research and it looks like any problems with the TCC would not occur when i am idle sitting still with a warm engine. It seem most issues with the TCC occour when you are driving. When i am driving my car is smooth as the day i bought it.

Am I missing something?

Thanks for the tip. But i was doing some research and it looks like any problems with the TCC would not occur when i am idle sitting still with a warm engine. It seem most issues with the TCC occour when you are driving. When i am driving my car is smooth as the day i bought it.

Am I missing something?

No youre probly not missing anything, I was only speculating what the problem could be.

How old are your plugs and wires?
Hav you tried any fuel sytem cleaners?
Hav you checked for any vacum leaks on the intake?

Also the IAC (intake air control) could cause some rough idling if it needs cleaned.
TheIAC can build up carbon inside the TB and interfere with proper idle.

Just sounds like you both need(ed) and good tune up.

No youre probly not missing anything, I was only speculating what the problem could be.

How old are your plugs and wires?
Hav you tried any fuel sytem cleaners?
Hav you checked for any vacum leaks on the intake?

Also the IAC (intake air control) could cause some rough idling if it needs cleaned.
TheIAC can build up carbon inside the TB and interfere with proper idle.

Just sounds like you both need(ed) and good tune up.

Plugs were replaced about 30,000 miles ago, have not checked them lately, but I replaced them with Platnuim plugs. I used to drive 140 miles a day which is y i have so many miles on the car.

The car does not have plug wires.

I have not run an fuel cleaner in it right now, but i do have a bottle of Fuel Injector Cleaner i am going to run in it next fill. During the life of the card i have run that stuff throught it many times.

I jsut replaced the air filter last week.

I have not checked for any vacuum leaks but it has been suggested, i guess i need to do it.

I get teh weird feeling it has something to do iwth the tranny as the engine seems smooth at all times, never misses or anything. The car simply seems like it "Vibrates" to much when it is warmed up and in a forward gear idleing. When driving or out of gear or in reverse it is smooth.

I also jsut had an oil change and i do about every 3,000 to 4,000 miles. For the most part the car has been babyed.

Ya your 4cyl doesnt hav wires.
But their is boots in there, and they do go bad.
Probly more offten then a V6, because they are covered inside a very hot spot :grinyes:

Vacum lines could just hav a crack or something not obvious at first until you giv them a thurough going over.

But, if youre just having the roughness in forward gear(s), I'd check the trany mount(s) and engine mounts.
They could be broken and letting the motor jump excessivly :dunno:

The only other times I've seen engines jump is when they hav a bad misfire, or the timings off.

Also if you used just plain Platnuim plugs, that could be some of the problems, they burn up quick.
Iriduim Platnuim are what GM recomends these days, Iridiums the hardest metal on earth(next to the Hords Of Nebulah) :lol:


Hope that helps,
and Good Luck

Ya your 4cyl doesnt hav wires.
But their is boots in there, and they do go bad.
Probly more offten then a V6, because they are covered inside a very hot spot :grinyes:

Vacum lines could just hav a crack or something not obvious at first until you giv them a thurough going over.

But, if youre just having the roughness in forward gear(s), I'd check the trany mount(s) and engine mounts.
They could be broken and letting the motor jump excessivly :dunno:

The only other times I've seen engines jump is when they hav a bad misfire, or the timings off.

Also if you used just plain Platnuim plugs, that could be some of the problems, they burn up quick.
Iriduim Platnuim are what GM recomends these days, Iridiums the hardest metal on earth(next to the Hords Of Nebulah) :lol:


Hope that helps,
and Good Luck

I'll take a look at the plugs again, I also considered replacing the motor mounts (i thought about that too but it still bewilders me y it only happens in forward gears and not reverse, taht is y i did do it yet).

The boots would be good to look at as well, but again I am starting to lean towards something in the tranny. I may take it in for a diagnosis my next oil change.

Sounds like a plan.

Your Aleros 4cyl powertrain has 4 mounts !
Front and rear mounts(lower), driverside and passenderside (upper).

It probly wouldnt hurt getting it scanned with the proper scanning Tool(s).

i have a similar problem,,found cracked vacum hose on map sensor ,,still idles rough and seems to purge while idleing in drive,havent changed plugs,havent even seen them ,,,i have learned something from this post,,,the 2.4 does not have spark plug wires.

I have an 01 Alero and it had a hard time idling and didn't seem to have a whole lot of power but a friend of mine who happens to be a mechanic told me to buy this cleaner called sea foam and remove the large vacuum hose off the brake assist diafram (recommend u take the hose off then start the car) and while the car is running let the vacuum suck more than half the can of sea foam in. without that hose on the idle will run like shit and the rpms had to be kept up about 1000 to 1500 so it wouldn't stall while pouring the sea foam in. its suppose to clean off the valves in the engine and blow out all the carbon out the tail pipe. it had some pretty nasty smoke coming out the back while i was doing this which i was told can vary depending on how dirty it is inside the engine. (Important!: make sure u replace the hose before u try driving it because to my understanding you wont have power brakes if you don't) it took about half hour to 45 minutes to get the majority of the can in and i put the rest of it in the gas and took it out on the high way and basically drove it like i stole it with nasty smoke flying out, but after all that its been running like a dream ever since! my friend called this every mechanics basic tuneup and best of all it will work on any vehicle as long as u find the right hose anyways lol. I definitely noticed more power while accelerating and my gas mileage increased from about 20 mpg to 23 to 24ish mpg so i am really happy with the result =) Hope this helps! as an extra he recommended this oil treatment called slick 50 which i guess regenerates the piston rings and seals small cracks and coats the inside of the oil box with a Teflon like surface to reduce heat and friction. after that i noticed my heat gauge would sit near a quarter inch below normal operating temp during regular driving so i assume its doing its job.

Do you work for AutoZone, NAPA, Advance, etc., by any chance?:tongue: