It's been happening for about a year now. Between 1000 and 2000 rpm the car will stumble and act like it's running really rich. I have replaced the spark plugs, map sensor, o2 sensor, coolant temp sensor and even tried a different EGR valve and had the Ignition module tested. I have never had the CEL come on. Nothing has fixed it yet. It does it in the winter and summer. Doesn't matter if the car is cold or hot. Still does the same thing. What I can't understand that after 2000 rpms the car runs great. Gas mileage is fine. When it starts running rich there's a liquid that drips out of the exhaust that really has no smell. I'm not loosing coolant and not that burning oil from what I can see. What could be the cause?

I am having somewhat of the same problem check HERE


96 CAVALIER Z24 UNDER CONSTRUCTION

Replace the boots that go over the spark plugs...

I was having a similar issue with my 98 Z. It would spit and sputter until I got over the 2k mark and then it would straighten out. I tried a fuel filter, my CEL light was coming on with a bad downstream 02 sensor so I replaced that, and nothing had worked. I replaced those boots and it runs great now...

yeah that could work too just talka all precautions


96 CAVALIER Z24 UNDER CONSTRUCTION

How abou the fuel system, Has the injectors had a O rings serviced, How about the fuel filter, How long has it been since it was changed?. I would also look for leaks in the In the intake manifold.

Good Luck.

Sounds like the TPS cant position the throttle between those rpms.
Just my guess....
Hope it helps.






...They just HATE it when you ...POINT - LAUGH - then DRIVE OFF AND AWAY-!...

I just installed a new fuel filter about 3 months ago. Also the upper O2 sensor that I just replaced was replaced with a Bosch. I wanted an ACDelco but the guy at the shop said that the Bosch would work. And since I changed the O2 when starting the car after about 2 minutes of idling it tries to stumble and cut off. I think that the new O2 may be part of the problem also. I will replace the spark plug boots and order a new ACDelco O2 and see it that helps. Anything else to look for?

I used a Bosch sensor and it worked fine for me...

So you had the same problem with the stumble and the boots fixed it. I'm going to pick up some boots from O'Reillys today and see what happens.

Well I just tried the boots and it needed them but I still have the stumble. I read that the coil packs should have 10,000ohms (10.0) of resistance. So I checked the resistance with my multi-meter and one of them read 6.99 and the other 6.88. Has anyone tested their coils before? I just turned the coils over and stuck the leads into the two open holes that connect to the housing. Should they be different? Please let me know.

Okay Im going to try again...
Have you tried replacing the TPS???

if the TPS cant read the throttle position in that rpm range, your car will throw fuel without enough air, thus the resemblance of running rich.

Sometimes the little thing cause big problems...








...They just HATE it when you ...POINT - LAUGH - then DRIVE OFF AND AWAY-!...

All Flawless wrote:Okay Im going to try again...
Have you tried replacing the TPS???

if the TPS cant read the throttle position in that rpm range, your car will throw fuel without enough air, thus the resemblance of running rich.

Sometimes the little thing cause big problems...

YES I have tried a TPS. No change. I had a problem with My TPS about 2 years ago. Replace it with a new ACDelco and my problems were fixed. I have also used a meter and tested the current running through the TPS at different openings and everything checked out.

Check to see that the housing under the idi cover is not cracked. If it is then there is your problem. Most likely case on 2.4's, the housing cracks and it throws a fit.

Well from what I can tell the housing looks fine. I also tested to make sure I could get a signal through each terminal. If someone would be able to check their coils to see if mine are bad that would really help me out. I'm even thinking of the 2.2 coil conversion that team green is working on right now. If they were bad this would be a perfect time to do it.

Does anyone have a set of coils that they can check to see what ohms that you get out of them. Like I said above mine was 6.88 on one and 6.99 on the other. Are my coils bad?

Well, I'm having a similiar problem. I suspected coils as well. Mine come in at 5.78. Hanes manual says they should be between 5 to 7, so you are definately on the edge, but I don't know if that would be bad enough to cause your probs. Good luck.

Well I took my car to the stealership and they told me that everything checked out fine but my fuel pump. It was running about 10psi low. They tried to change the FPR and it didn't help. So they suggested that the fuel pump must be bad. So I ordered one from Mr.Fuelpump from E-bay for $200.00 with a warranty. I'll let you guys know if it fixes the problem.

Good luck, hope that fixes it...

Let me know if that is the prob because i have the same crap at 2500 rpm. I replaced the coils and its still the same. I found that if you run the higher grade gas the hand(i call it) is shorter.

Let me know if that fuel pump fixed it.


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Well I replaced the fuel pump today and my car still has the stumble. I'm stumped and pissed. Stumped at what it could be and pissed that the stealership guys told me that without a shadow of a doubt that the fuel pump was the problem. I think that they was just wanting me to pay them to change it and then when it didn't work they would say that it was something else. Next step check for a vacuum leak.

Hello Gents:

Maybe my situation will shed some light for you.
I own a 00 Z24 with 47K miles. It started sputering, somewhat like you mentioned, about a month ago. I also got the intermitent Cyl misfire code and the Bank 1 O2 sensor error. Gas millage was really bad too. About 18mpg on city at best.
The 02 error was due to a loose cable on the connector (the cable is kinda stretched since I put in a pacesetter header). I lenghten the 02 leads and the problem was solved but I was still getting the intermitent cyl #3 misfire code. I got the coil housing out and tested the coils like you mentioned and got 6.98 and 6.99 on each. I tested the wiring harness for the coils and checked out fine too.
I went ahead and switched the positions of the coils inside the housing to see if there was any difference in the # cylinder. The error continued with the exact same Cylinder # so the coils were not the issue. I was on a long trip and all of the sudden the car started sputering really bad, like I was only running on 2 cylinders. I limped home (about 20 miles and 1/2 tank of gas later).

Needless to say, I shot the Cat converter. As you may know, the cat converter is in charge of burning any exess unburned fuel. If you pass too much fuel through it, the aluminum mesh will just reach melting point and get clogged up.

In the end, the culprit for my problems was the coil housing (the white plastic housing where the coils are). This housing replaces the traditional spark plug wires on any other "normal" car. If you test the housing from the spark plug contacts to each of the coil terminals inside of it, you may notice that some of them may have developed resistance to voltage. Some terminals (in my case, the 1 and 3 cyl connections) will only register 5-6 volts on the other end when you put 12V of electricity through it. This part should be available at your nearest autoparts. In my case, it cost me around 82 dollars (at Advanced Auto Parts or PepBoys in Puerto Rico). I have to add the cost of a new High Flow Cat Converter ($125). The car runs like a tiger now and all signs of sputering went away.

Hope this helps,

Fred Larracuente
Guaynabo, Puerto Rico USA

Well I tested the coil housing it's getting voltage just fine. Something that I noticed today was that my voltage gauge would drop from 14.4 to somewhere around 13.5 when I accelerate hard. The alternator is charging and the battery is in great condition. What would cause this?

I also have this problem.. it seems when your at lower rpm (under 4200ish) it bogs. I changed my plugs, cleaned my intake, streched my springs in the boots to give better contact. But I still get this problem. Sometimes I get PO141 and sometimes PO420 and sometimes it comes together.

Well I have fixed the weird idle problem but still have the stumble/hesitation problem. I changed the new Bosch O2 for the ACDelco and that fixed the idle. Can your ignition cause your car to stumble at low rpms and run fine at high rpms. Also I checked vacuum with a vacuum tester and it tested out fine. Could a partially clogged cat cause low RPM stumble? My gas mileage has also dropped to 25mpg from 32mpg. I did change out the TPS with a new ACDelco also. I'm really stumped right now. Tired of spending money on it.

Well my car is fixed. I replaced the ignition housing and the ignition coils and now everything is fine. Thanks for all the help with this problem.