Well first of you are dealing wit a 2000 cavalier z24 manual wit only 75000 on er. well i have a rksport 4-2-1 header on it along wit custom 2.25 exaust straight through no cat needed ive heard this several times so no thats not the prob. well i have gone through one new computer swap refash it helped a lil bit then i replace both the o2 sensors that helped a bit. after this alls my car does is it studders when you hit second gear or put a load on it at low rpms and you kind lose throttle rsponse till you floor it. i took it to a shop and they had it for a month and everything is ok all the sensors and the puter are all working fine. he thought maybe it was the o2 simulator acting up that elliminates the last 02 remember. if you guys have any ideas i would like to hear them rip all you want i just need some help laters peace

I would think its a computer calibration problem. I had a similar problem due to a cam position sensor that was bad. It did not throw an engine code, but had the timing all screwey. If you are running rich as well, this could be your prob, too.

Also, you say that you have eliminated the catalytic converter, gotten a reflashed computer, and are running an o2 simulator in place of the after cat sensor. Well, most performance computer reflashes and "fake" sensors are tuned to give you increased performance under wide open throttle, but without much concession for daily driving. It very well could be that these ods are just not compensating correctly for part throttle operation, and causing the engine to do any number of things when you are at partial throttle, including momentarily going full rich, retarding ignition timing, etc. Problems like this could cause the engine to stumble when shifting or at part throttle/low rpm conditions.

You may want to check with the manufacturers of your aftermarket computer and sensor to see if the products were tuned for part throttle operation.




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When American astronauts first went into space, they discovered their pens wouldn't write. So the government spent $30 million to develop a pen they could use in space........ The Russians used a pencil.

wow thanks alot i dunno tho im soo lost when it comes to this car its such a lemon but yet again it had raced a s/c cavy and beaten it by like a car length lol im bout ready to sell her. is there someway i could reflash it and cause this stumble to go away????

If you are still running the stock computer (reflashed), you can go to Autozone, use their code reader, and see if it threw any codes for fuel system, cam timing, etc. Even if the engine light isn't showing, it will still record codes it has given in the past until the system is cleared manually, so you should be able to check its history. If your computer is actually an aftermarket piece, then you may not be able to check for engine codes.

Otherwise, I would say the next most logical thing is the O2 simulator, and you may want to reinstall a catalytic converter and a real O2 sensor. A lot of the engine's fueling and timing maps are dependent on the signals received from these sensors and the simulator may not be able to simulate the full range of operation of a real sensor with enough resolution to operate normally, so it would throw off the computer's calculation, making it suddenly overcompanate. Your computer (reflashed stock or aftermarket) should be able to be retuned to compensate for this, but it would probably cost more than just putting in a cat and regular O2 sensor.

There is no absolute guarantee this is the problem. These "glitches" are always the second hardest thing to chase down on a car (the hardest are ususally sounds). Especially a modified one... But if you are going to sell the car, you may want to put those parts on anyway. I don't know where you live, but here in California, a car has to be smogged once sold, and the buyer may not like having to spend extra $$$ to get the necessary equipment installed. Instaling it before the sale could help you get more for the car...

On the other hand, if you already have a decent chunk of change for a new ride, sell it as is for a low price and let it be somebody else's problem to figure out the problem and get it smog ready.


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When American astronauts first went into space, they discovered their pens wouldn't write. So the government spent $30 million to develop a pen they could use in space........ The Russians used a pencil.

wow thanks. yeah well the computers a stock new one out of a wrecked car i checked everything the numbers the year and even checked at the dealer he said it would work. well here is the think as soon as i put the new puter in it ran great no probs no studering well a lil bit no codes came up. well i was drivin up north to visit wit my rents and i was passing a semi up a hill kicked it down and the check engine light came on. so i dunno if i had a misfire or what. so where is the cam position sensor located on this engine. well i have a magnaflo high flo cat so i was waitin on that cause my car really opened up when i took the cat off. better milage not to mention i beat a supercharged cavalier hows that work. thats why i call it the freak lemon its fast for some odd reason. well thanks for the help and good luck wit your cavy peace