First, i am talking about 1998 Cavy Z24 manual. This car has had this problem since i got it 4 years ago it does seem to be getting worse now. I have no check engine light and i have checked it with a computer it is not giving any codes. When i start the car it idles fine and sounds fine but if i go to move or if i sit long enough the rpms with go up and down between under 1 and up to 3. If i give it gas and sit for awhile it will eventually stop ideling funny and run normal, but if i go to leave it almost stall and sometimes lately it does stalls. It does not matter if its cold or warm out it will still act this way. Over the last 2 years i have replaced a lot of things:

Fuel Filter
Engine Coolant Temperature Sensor (ECT)
Intake Air Temperature Sensor (IAT)
Throttle Position Sensor (TBS)
Manifold Absolute Pressure Sensor (MAP)
02 Sensor before cat (10-2007)

Things i was told it could be and people whom also had this problem told me to try... well nothing works. I love my car but i can't stand when you go to pull out and it acts like that and stalls its embarassing. i have taken her to the dealer and they do not know they ask it could be this and that but i am not paying a dealer to "try" and figure it out. Any ideas????

Check the idle air control motor and its bore. Clean both with a few good shots of throttle body cleaner, may end up having to replace the IAC itself. After you clean them and have the IAC reinstalled, check for vacuum leaks with whats left of the TB cleaner, IE with the motor running spray it around vacuum connections, the throttle body base, anywhere that vacuum could possibly leak. If the idle changes consistently at a certain spot, suspect a vacuum leak and go from there.

But if it was a vacuum leak i would think she would idle like this all the time...she only does this when i start her while i am driving she runs great??

O2 sensor..theres like 50 million posts about this on here and each time it ends up being the same thing...the car idles fine for the frist couple minutes then when the car goes into closed loop it idles funny and the more gas you give it the more itll want to die..let it idle funny for a couple minutes and itll go back to normal...sound familiar??? your #1 02 needs replaced and replace it with an AC DELCO ONLY!!! if you use another brand youll probably end up with the same problem..new or not...that might even be whats wrong now....it usually will NOT throw a code so dont let that fool you

Yeah i did replace the o2 sensor with one from auto zone... i did read about the ac delco one but its like $80 from gm... what is so special about it? What is the difference that it would actually fix my problem?? i figured it the cheapie would not fix my problem why spend $80 on the same thing that will not work either...

the difference is the gm one will make your car run correctly again...and by telling me you changed it with a bosch one from auto zone confirms that its the problem....dont know about 80 bucks..id look around, maybe ebay or something but thats the part you need..maybe it has to do with how fast it heats up when cold???? who knows...i just know an ac delco o2 fixes the problem everytime....it took me a year to realize this when MINE was doing it and i wasted ALOT of money trying other things to fix it...till i found out it was just the wrong brand

okay thanks for your help, i do not know when i will get it changed though my b/f just did the o2 sensor about a week ago... i dont think he will want to redo it.. i was gunna get the ac delco one i just did not see the difference and the price difference too.

I think I read somewhere that NGK/NTK makes the O2 sensors for GM, I may be wrong though. Those can be had on eBay for very reasonable prices. As for Bosch, there are many opinions. USUALLY when the 1st O2 sensor is acting up, it will trip a code, but not always. Bosch is pretty much hit or miss with some of its parts, especially spark plugs. Complete junk in my opinion. Never had any experience with their O2 sensors though.

I have a 98 sunfire, it was doing the exact same thing. I replaced the o2 sensor because that's what the trouble code said. that helped a little bit. I bought the bosch from auto zone and it help a little bit. still couldn't get it right.

So I took the car and had a computer diagnostic done. the problem... I had a spark plug wire that was arcing. check your wires and plugs because that can be a problem to.

Does anyone know where the cheapest place is to get an ACDELCO O2 Sensor??? I found one on Auto Parts Giant website for $56.42 with shipping, and i found one on GM Parts Direct for $56.72 with shipping. But Auto Parts Giant states that the sensor is an ACDELCO. On GM Parts Direct it does not state that it is an ACDELCO. I am figuring it should be because it is from GM but i have been emailing (only way to contact) them for an answer and no one is responding.. so does anyone know what O2 sensor GM Parts Direct would be using? Thanks!

I've had a Bosch 1-wire sensor in my 98 for years now. No problems.

Once your idle is stable, unplug your IAC motor and see if your problems continue.

2002 Cavalier 2200 5spd

I chased this problem on my 91 cav and finally found the PCV valve had lost the o-ring seal and vacuum was bypassing the valve, its worth checking out...my PCV has o -ring on top of it and on bottom of it...dont know if newer ones are the same.

I order an ac delco o2 sensor it is to be here on Monday... i will let you know if it fixes the problem.

Holy Crap....I can't believe an AC DELCO sensor is any different then a bosch but MY problem is fixed! I have had that problem for 4 years since i own the car and hated it! Finally I can get in my car and do not have to worry about it idleing like crap and stalling. THANKS A LOT GUYS!!!!!!